LibGfx: Make Color::from_string() case-insensitive

This function implements CSS color syntax, which is case-insensitive in
HTML contexts. Making it insensitive here means not having to remember
to do it in every user, (many of the HTML elements do not do this,) and
means they don't have to produce a lowercase copy of the input string
before passing it.

Userland/Libraries/LibGfx/Color.cpp

@@ -30,7 +30,7 @@ String Color::to_string_without_alpha() const
 
 static Optional<Color> parse_rgb_color(StringView const& string)
 {
-    VERIFY(string.starts_with("rgb("));
+    VERIFY(string.starts_with("rgb(", CaseSensitivity::CaseInsensitive));
     VERIFY(string.ends_with(")"));
 
     auto substring = string.substring_view(4, string.length() - 5);
@@ -51,7 +51,7 @@ static Optional<Color> parse_rgb_color(StringView const& string)
 
 static Optional<Color> parse_rgba_color(StringView const& string)
 {
-    VERIFY(string.starts_with("rgba("));
+    VERIFY(string.starts_with("rgba(", CaseSensitivity::CaseInsensitive));
     VERIFY(string.ends_with(")"));
 
     auto substring = string.substring_view(5, string.length() - 6);
@@ -245,18 +245,18 @@ Optional<Color> Color::from_string(StringView const& string)
         { 0x000000, nullptr }
     };
 
-    if (string == "transparent")
+    if (string.equals_ignoring_case("transparent"))
         return Color::from_rgba(0x00000000);
 
     for (size_t i = 0; !web_colors[i].name.is_null(); ++i) {
-        if (string == web_colors[i].name)
+        if (string.equals_ignoring_case(web_colors[i].name))
             return Color::from_rgb(web_colors[i].color);
     }
 
-    if (string.starts_with("rgb(") && string.ends_with(")"))
+    if (string.starts_with("rgb(", CaseSensitivity::CaseInsensitive) && string.ends_with(")"))
         return parse_rgb_color(string);
 
-    if (string.starts_with("rgba(") && string.ends_with(")"))
+    if (string.starts_with("rgba(", CaseSensitivity::CaseInsensitive) && string.ends_with(")"))
         return parse_rgba_color(string);
 
     if (string[0] != '#')