glsl: Convert ir_binop_vector_extract in the LHS to ir_triop_vector_insert

glsl: Convert ir_binop_vector_extract in the LHS to ir_triop_vector_insert

The ast_array_index code can't know whether to generate an
ir_binop_vector_extract or an ir_triop_vector_insert.  Instead it will
always generate ir_binop_vector_extract, and the LHS and RHS have to be
re-written.

v2: Convert tabs to spaces.  Suggested by Eric.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>