LibGfx: Make BMP decoder always produce BGRA8888 or BGRx8888 bitmaps

This was the only remaining codec that produced IndexedN bitmaps.
By removing them, we'll be able to get rid of those formats and simplify
the Bitmap and Painter classes.

Userland/Libraries/LibGfx/ImageFormats/BMPLoader.cpp

@@ -1247,13 +1247,10 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
 
         switch (bits_per_pixel) {
         case 1:
-            return BitmapFormat::Indexed1;
         case 2:
-            return BitmapFormat::Indexed2;
         case 4:
-            return BitmapFormat::Indexed4;
         case 8:
-            return BitmapFormat::Indexed8;
+            return BitmapFormat::BGRx8888;
         case 16:
             if (context.dib.info.masks.size() == 4)
                 return BitmapFormat::BGRA8888;
@@ -1314,14 +1311,10 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
                 while (column < width && mask > 0) {
                     mask -= 1;
                     size_t color_idx = (byte >> mask) & 0x1;
-                    if (context.is_included_in_ico) {
-                        if (color_idx >= context.color_table.size())
-                            return Error::from_string_literal("Invalid color table index");
-                        auto color = context.color_table[color_idx];
-                        context.bitmap->scanline(row)[column++] = color;
-                    } else {
-                        context.bitmap->scanline_u8(row)[column++] = color_idx;
-                    }
+                    if (color_idx >= context.color_table.size())
+                        return Error::from_string_literal("Invalid color table index");
+                    auto color = context.color_table[color_idx];
+                    context.bitmap->scanline(row)[column++] = color;
                 }
                 break;
             }
@@ -1333,14 +1326,10 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
                 while (column < width && mask > 0) {
                     mask -= 2;
                     size_t color_idx = (byte >> mask) & 0x3;
-                    if (context.is_included_in_ico) {
-                        if (color_idx >= context.color_table.size())
-                            return Error::from_string_literal("Invalid color table index");
-                        auto color = context.color_table[color_idx];
-                        context.bitmap->scanline(row)[column++] = color;
-                    } else {
-                        context.bitmap->scanline_u8(row)[column++] = color_idx;
-                    }
+                    if (color_idx >= context.color_table.size())
+                        return Error::from_string_literal("Invalid color table index");
+                    auto color = context.color_table[color_idx];
+                    context.bitmap->scanline(row)[column++] = color;
                 }
                 break;
             }
@@ -1353,19 +1342,13 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
                 u32 high_color_idx = (byte >> 4) & 0xf;
                 u32 low_color_idx = byte & 0xf;
 
-                if (context.is_included_in_ico) {
-                    if (high_color_idx >= context.color_table.size() || low_color_idx >= context.color_table.size())
-                        return Error::from_string_literal("Invalid color table index");
-                    auto high_color = context.color_table[high_color_idx];
-                    auto low_color = context.color_table[low_color_idx];
-                    context.bitmap->scanline(row)[column++] = high_color;
-                    if (column < width) {
-                        context.bitmap->scanline(row)[column++] = low_color;
-                    }
-                } else {
-                    context.bitmap->scanline_u8(row)[column++] = high_color_idx;
-                    if (column < width)
-                        context.bitmap->scanline_u8(row)[column++] = low_color_idx;
+                if (high_color_idx >= context.color_table.size() || low_color_idx >= context.color_table.size())
+                    return Error::from_string_literal("Invalid color table index");
+                auto high_color = context.color_table[high_color_idx];
+                auto low_color = context.color_table[low_color_idx];
+                context.bitmap->scanline(row)[column++] = high_color;
+                if (column < width) {
+                    context.bitmap->scanline(row)[column++] = low_color;
                 }
                 break;
             }
@@ -1374,14 +1357,10 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
                     return Error::from_string_literal("Cannot read 8 bits");
 
                 u8 byte = streamer.read_u8();
-                if (context.is_included_in_ico) {
-                    if (byte >= context.color_table.size())
-                        return Error::from_string_literal("Invalid color table index");
-                    auto color = context.color_table[byte];
-                    context.bitmap->scanline(row)[column++] = color;
-                } else {
-                    context.bitmap->scanline_u8(row)[column++] = byte;
-                }
+                if (byte >= context.color_table.size())
+                    return Error::from_string_literal("Invalid color table index");
+                auto color = context.color_table[byte];
+                context.bitmap->scanline(row)[column++] = color;
                 break;
             }
             case 16: {
@@ -1468,12 +1447,6 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
         }
     }
 
-    if (!context.is_included_in_ico) {
-        for (size_t i = 0; i < context.color_table.size(); ++i) {
-            context.bitmap->set_palette_color(i, Color::from_rgb(context.color_table[i]));
-        }
-    }
-
     context.state = BMPLoadingContext::State::PixelDataDecoded;
 
     return {};