Prior to this commit, when "OpName %id name" was encountered, the info
corresponding to "name" was immediately associated with %id.  This is
not necessarily correct because there could be multiple ids with the
same name.  For example a sampler declaration and an unrelated function
argument could have the same name.  In this case, the sampler
declaration and function argument name don't even need to be in the same
shader stage.

This change modifies the SPIR-V transformation such that the name-id
mapping is tracked until the OpVariable instruction that actually
declares the variable is visited.  The mapping to variable info is only
done if the storage class specified in this instruction corresponds to a
shader interface variable.

Bug: angleproject:3394
Change-Id: I35a1f6f8278e4b1ad81c9955a55e1b72d6f2e4ea
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2057248Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>