ngl: move uniform key mapping into uniform state

ngl: move uniform key mapping into uniform state

Previously, we translated the uniform key (an enum) into a location within
the shader program in GskNglProgram. A number of performance improvements
were focused around having low nubers for the uniform locations. Generally
this is the case, but some drivers such as old Intel drivers on Windows
may use rather large numbers for those.

To combat this, we can push the translation of uniform keys into locations
at the GskNglUniformState level so that we work with unranslated keys
through the process until applying them.

Fixes #3780