glsl: Process redeclarations before initializers

glsl: Process redeclarations before initializers

If an array redeclaration includes an initializer, the initializer
would previously be dropped on the floor.  Instead, directly apply the
initializer to the correct ir_variable instance and append the
generated instructions.

Fixes bugzilla #34374 and piglit tests glsl-{vs,fs}-array-redeclaration.

NOTE: This is a candidate for stable release branches.  0292ffb8 and
8e6cb9fe are also necessary.