Actually GlyphItem should be VCL internal, but this requires a
transparent SalLayoutGlyphs (i.e. via pImpl), which I'm too lazy
to implement currently.

This seperation makes the affected source files more obvious and
later migration of vcl/glyphitem.hxx easier.
While at it apply the coding style and add '_' to member prefix.

Change-Id: I61497af5c628c40f51597ce0ef286c47321acbc2
Reviewed-on: https://gerrit.libreoffice.org/62358
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>