Vulkan: Refactor ID-discovery out of SPIR-V transformer The SPIR-V transformer performs multiple transformations in one pass. This is the first of a series of refactoring changes that detangle these transformations and encapsulate them, while allowing the transformation to remain single-pass. Bug: angleproject:4888 Change-Id: I327f693d99496a0b89028abe627119e4a2b07c42 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2702651 Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>