mesa: rework GLSL array code generation

mesa: rework GLSL array code generation

We now express arrays in terms of indirect addressing.  For example:
  dst = a[i];
becomes:
  MOV dst, TEMP[1 + TEMP[2].y];
At instruction-emit time indirect addressing is converted into ARL/
ADDR-relative form:
  ARL ADDR.x, TEMP[2].y;
  MOV dst, TEMP[1 + ADDR.x];
This fixes a number of array-related issues.  Arrays of arrays and complex
array/struct nesting works now.
There may be some regressions, but more work is coming.