[Fonts] initiateFontLoadingByAccessingGlyphDataIfApplicable() operate…

…s on code units, not code points

https://bugs.webkit.org/show_bug.cgi?id=260768
rdar://114488476

Reviewed by Cameron McCormack.

It's meaningless to lookup fonts using individual surrogates.

* Source/WebCore/rendering/RenderText.cpp:
(WebCore::initiateFontLoadingByAccessingGlyphDataIfApplicable):

Canonical link: https://commits.webkit.org/267333@main

Source/WebCore/rendering/RenderText.cpp

@@ -311,8 +311,8 @@ static void initiateFontLoadingByAccessingGlyphDataIfApplicable(const String& te
         fontVariant = NormalVariant;
     }
 #endif
-    for (size_t i = 0; i < textContent.length(); ++i)
-        fontCascade.glyphDataForCharacter(textContent[i], false, fontVariant);
+    for (UChar32 character : StringView(textContent).codePoints())
+        fontCascade.glyphDataForCharacter(character, false, fontVariant);
 }
 
 void RenderText::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)