Implement fixes for built-in block member ambiguities across multiple specifications

It was not always clear which built-in variables are supposed to be in which built-in block (or not at all). There were both specification issues and glslang issues related to this.

Much work was already done in glslang to address the progress in this space, and this issue is meant to help finish it all off.

Review the existing glslang work and the relevant built-in block specifications first; the issue does not identify specific files, tests, or entry points. Compare the remaining specification and implementation discrepancies, then confirm that built-in variables are assigned consistently across all affected specifications and glslang behavior.

Written by the indexing model from the issue text.