Revert two shader layout changes to fix regressed dEQP tests
Reverts two commits to fix the regressed dEQP tests described #266 (closed):
c5f118c8ff1 2022-06-02 shader: Remove layout_location field [needed to fix the build after previous revert]
99f8cd3dc0c 2022-05-26 shader: remove obsolete layout handling code [bisection flagged as the cause of regression]If we can't arrive at a solution to #266 (closed), I'd request landing this revert to fix the tests in the meantime.