With this initial implementation, it's possible to get precision
qualifier mis-matches in the generated GLSL 4.50. According to the
spec this is allowed. From GLSLangSpec 4.50 section 4.7 "Precision and
Precision Qualifiers":

For the purposes of determining if an output from one shader stage
matches an input of the next stage, the precision qualifier need not
match.

However, when converted to SPIR-V and run through the shader validation
any mismatches will cause shader validation errors. Initially just
ignoring those errors with this commit.

Bug: angleproject:3078
Change-Id: Ia2b04f90f0a7b6b1302c1b1b3e32bcfd8db9ed49
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2057749Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>