Drop the special / duplicate glyph rect bound cache implementation
for Freetype fonts. The GlyphCache class now looks a lot like the
ImplFontCache class.

The lru handling for Freetype fonts is based on the byte / memory
size, including the glyth bound-rect caching. Using the new common
cache is effectivly removing the bound-rects from this accounting,
so the garbage collection won't free them anymore.

Change-Id: Ie53226596ee2287e1059a74885f52c3d64bbccaa
Reviewed-on: https://gerrit.libreoffice.org/61377
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>