Bug 1884909 - Resolve the real family name during CoreTextFontList::InitSystemFontNames, so that font fallback finds it as expected. r=gfx-reviewers,bradwerth

This restores the equivalent behavior of GetRealFamilyName in the old Cocoa-based code
that we used prior to bug 1884314.
(See https://hg.mozilla.org/mozilla-central/annotate/02aeca6d94b127379287a276a0f0d7958dc4efaa/gfx/thebes/gfxMacPlatformFontList.mm#l415)

Dropping this function during the migration from Cocoa to Core Text APIs meant that the
macOS system font was recorded under the "virtual" family name .AppleSystemUIFont
instead of its "real" name .SF NS. This seemed harmless enough, but not quite... it
interferes with finding the system font in CoreTextFontList::PlatformGlobalFontFallback,
if that's the font that Core Text chooses to return for a given character.

As a result, the bugs/1721223-1.html testcase changed from using the system font
to finding and loading a Meetei Mayek font (at least on my system) that also happens
to include the subscript-s letter; but that fallback happens asynchronously as this
font hasn't yet been initialized, and that broke the test.

This restores the prior behavior, by porting the GetRealFamilyName functionality to
the Core Text-based implementation.

Differential Revision: https://phabricator.services.mozilla.com/D204590

Author: jfkthame

gfx/thebes/CoreTextFontList.cpp

@@ -1863,11 +1863,26 @@ void CoreTextFontList::ReadFaceNamesForFamily(
   }
 }
 
+static CFStringRef CopyRealFamilyName(CTFontRef aFont) {
+  AutoCFRelease<CFStringRef> psName = CTFontCopyPostScriptName(aFont);
+  AutoCFRelease<CGFontRef> cgFont =
+      CGFontCreateWithFontName(CFStringRef(psName));
+  if (!cgFont) {
+    return CTFontCopyFamilyName(aFont);
+  }
+  AutoCFRelease<CTFontRef> ctFont =
+      CTFontCreateWithGraphicsFont(cgFont, 0.0, nullptr, nullptr);
+  if (!ctFont) {
+    return CTFontCopyFamilyName(aFont);
+  }
+  return CTFontCopyFamilyName(ctFont);
+}
+
 void CoreTextFontList::InitSystemFontNames() {
   // text font family
   AutoCFRelease<CTFontRef> font = CTFontCreateUIFontForLanguage(
       kCTFontUIFontSystem, 0.0, nullptr);  // TODO: language
-  AutoCFRelease<CFStringRef> name = CTFontCopyFamilyName(font);
+  AutoCFRelease<CFStringRef> name = CopyRealFamilyName(font);
 
   nsAutoString familyName;
   GetStringForCFString(name, familyName);