mesa: add EXT_dsa indexed texture commands functions

mesa: add EXT_dsa indexed texture commands functions

Added functions:
  - EnableClientStateIndexedEXT
  - DisableClientStateIndexedEXT
  - EnableClientStateiEXT
  - DisableClientStateiEXT

Implemented using the idiom provided by the spec:

        if (array == TEXTURE_COORD_ARRAY) {
          int savedClientActiveTexture;

          GetIntegerv(CLIENT_ACTIVE_TEXTURE, &savedClientActiveTexture);
          ClientActiveTexture(TEXTURE0+index);
          XXX(array);
          ClientActiveTexture(savedActiveTexture);
        } else {
          // Invalid enum
        }