OpGroupNonUniformBroadcast can be supplied either a constant value or an
intermediate. I've split this Op into a fast path for constants that use
the original code, and a slow path that handles intermediates.

Tests: dEQP-VK.subgroups.ballot_broadcast.*
Bug: b/169608683
Change-Id: Idc74f3fe7e906315c59cf5b3bf3a450046e37375
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/50671
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Sean Risser <srisser@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>