update release notes for Gallium
update release notes for Gallium

I am trying to be exhaustive, but still I might have missed tons of other
changes to Gallium.
(cherry picked from commit 968a9ec76eadf55e8b58171884e1175d7b8cf59a)

Conflicts:

	docs/relnotes-7.9.html

tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,KTXSoftware/glsl2agal,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,djreep81/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,metora/MesaGLSLCompiler,adobe/glsl2agal,zeux/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,metora/MesaGLSLCompiler,mcanthony/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,adobe/glsl2agal,jbarczak/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,KTXSoftware/glsl2agal,mcanthony/glsl-optimizer,mapbox/glsl-optimizer,adobe/glsl2agal,zeux/glsl-optimizer,KTXSoftware/glsl2agal,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer