LibEDID: Store manufacturer id instead of allocating on each call

This also let's us use a KString instead of a string when we're in the
Kernel, which opens the path for OOM-failure propagation.

Userland/Libraries/LibEDID/EDID.cpp

@@ -480,6 +480,12 @@ ErrorOr<void> Parser::parse()
         }
     }
 
+    u16 packed_id = read_be(&raw_edid().vendor.manufacturer_id);
+    m_legacy_manufacturer_id[0] = (char)((u16)'A' + ((packed_id >> 10) & 0x1f) - 1);
+    m_legacy_manufacturer_id[1] = (char)((u16)'A' + ((packed_id >> 5) & 0x1f) - 1);
+    m_legacy_manufacturer_id[2] = (char)((u16)'A' + (packed_id & 0x1f) - 1);
+    m_legacy_manufacturer_id[3] = '\0';
+
     return {};
 }
 
@@ -555,16 +561,9 @@ StringView Parser::version() const
 #endif
 }
 
-String Parser::legacy_manufacturer_id() const
+StringView Parser::legacy_manufacturer_id() const
 {
-    u16 packed_id = read_be(&raw_edid().vendor.manufacturer_id);
-    char id[4] = {
-        (char)((u16)'A' + ((packed_id >> 10) & 0x1f) - 1),
-        (char)((u16)'A' + ((packed_id >> 5) & 0x1f) - 1),
-        (char)((u16)'A' + (packed_id & 0x1f) - 1),
-        '\0'
-    };
-    return id;
+    return m_legacy_manufacturer_id;
 }
 
 #ifndef KERNEL

Userland/Libraries/LibEDID/EDID.h

@@ -88,7 +88,7 @@ public:
     static ErrorOr<Parser> from_framebuffer_device(String const&, size_t);
 #endif
 
-    String legacy_manufacturer_id() const;
+    StringView legacy_manufacturer_id() const;
 #ifndef KERNEL
     String manufacturer_name() const;
 #endif
@@ -453,6 +453,7 @@ private:
 #else
     String m_version;
 #endif
+    char m_legacy_manufacturer_id[4] {};
 };
 
 }