Deprecate QFont::ForceIntegerMetrics and QFont::OpenGLCompatible

The ForceIntegerMetrics flag was added in Qt 4.7 specifically because
of WebKit, which was rounding text metrics and getting mismatches
with the underlying font engine whenever it supported fractional
advances. For backwards compatibility with how the CoreText engine
worked before this, we added a flag to allow rounding all metrics.

Rounding advances gives very broken rendering and is hopefully not
used by anyone anymore, so lets remove this flag in Qt 6.

As for OpenGLCompatible, this flag is not used anywhere. I am
not exactly sure what this flag did, but all fonts are
"OpenGL-compatible" at this point.

[ChangeLog][QtGui][QFont] Deprecated QFont::ForceIntegerMetrics
and QFont::OpenGLCompatible, with the intention of removing them
in Qt 6.0.0.

Change-Id: I0a492c153348023f00d561bab8ab4b5104c6c7c4
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/text/qfont.cpp

@@ -1353,8 +1353,8 @@ QFont::StyleHint QFont::styleHint() const
     \value NoAntialias don't antialias the fonts.
     \value NoSubpixelAntialias avoid subpixel antialiasing on the fonts if possible.
     \value PreferAntialias antialias if possible.
-    \value OpenGLCompatible forces the use of OpenGL compatible
-           fonts.
+    \value OpenGLCompatible This style strategy has been deprecated. All fonts are
+           OpenGL-compatible by default.
     \value NoFontMerging If the font selected for a certain writing system
            does not contain a character requested to draw, then Qt automatically chooses a similar
            looking font that contains the character. The NoFontMerging flag disables this feature.
@@ -1373,8 +1373,8 @@ QFont::StyleHint QFont::styleHint() const
     \value PreferQuality prefer the best quality font. The font matcher
            will use the nearest standard point size that the font
            supports.
-    \value ForceIntegerMetrics forces the use of integer values in font engines that support fractional
-           font metrics.
+    \value ForceIntegerMetrics This style strategy has been deprecated. Use \l QFontMetrics to
+           retrieve rounded font metrics.
 */
 
 /*!

src/gui/text/qfont.h

@@ -80,8 +80,10 @@ public:
         PreferQuality       = 0x0040,
         PreferAntialias     = 0x0080,
         NoAntialias         = 0x0100,
-        OpenGLCompatible    = 0x0200,
-        ForceIntegerMetrics = 0x0400,
+#if QT_DEPRECATED_SINCE(5, 15)
+        OpenGLCompatible Q_DECL_ENUMERATOR_DEPRECATED = 0x0200,
+        ForceIntegerMetrics Q_DECL_ENUMERATOR_DEPRECATED = 0x0400,
+#endif
         NoSubpixelAntialias = 0x0800,
         PreferNoShaping     = 0x1000,
         NoFontMerging       = 0x8000