glsl: handle indirectly indexed input registers in linker

glsl: handle indirectly indexed input registers in linker

For example, if the fragment shader reads gl_TexCoord[i] with a
dynamic index we need to set all the InputsRead bits for all
texcoords.  We were already doing this for shader outputs.
Refactored the later code so inputs and outputs are handled with
similar code.

Fixes a swrast failure with piglit's glsl-texcoord-array.shader_test