Refactor float to int point size conversions once again

They will be also needed in wxFontInfo soon, so move them there and use
these functions from both wxFont and wxNativeFontInfo, as they can
depend on wxFontInfo but not the other way round.

No real changes.

src/osx/carbon/font.cpp

@@ -578,7 +578,8 @@ bool wxFont::Create(int pointSize,
 {
     AccountForCompatValues(pointSize, style, weight);
 
-    return Create((float)pointSize, family, style, weight, underlined, faceName, encoding);
+    return Create(wxFontInfo::ToFloatPointSize(pointSize),
+                  family, style, weight, underlined, faceName, encoding);
 }
 
 wxFont::~wxFont()