This patch tries to attach debug location of a branch/return instruction to its predecessor or the closing brace. If none could be found, no debug info should be emitted.
It is invalid if the same decoration is applied to the same id multiple
times. This adds a check before adding a decoration that the decoration
is not already in the list. If it is, then the duplicate is not added.
Fixes#3627
This adds or changes binding/location decorations in 100s of shaders.
It also allows more output (spv.register.autoassign.rangetest.frag)
due to allowing ioMap() to fail.
