Merge pull request #2344 from billhollings/gather-constoffsts-arg-buffs

MSL: Image gather ConstOffsets supports multiple address spaces.

Merge pull request #2317 from KhronosGroup/fix-2309

MSL: Handle missing FP16 trancendental overloads.

Merge pull request #2290 from KhronosGroup/fix-2287

MSL: Fix type hierarchy for extended vectors.

Merge pull request #2255 from KhronosGroup/pr-2247

HLSL: Fix issue with vec4 straddle rules in substructs.

Merge pull request #2218 from KhronosGroup/pr-2217

Merge PR 2217

Merge pull request #2178 from billhollings/arg-buff-fixes

Fix argument buffer padding when content includes arrays.

Merge pull request #2178 from billhollings/arg-buff-fixes

Fix argument buffer padding when content includes arrays.

Merge pull request #2147 from KhronosGroup/fix-2145

Fix misc bugs with mixed pointer/array types in buffers

Merge pull request #2147 from KhronosGroup/fix-2145

Fix misc bugs with mixed pointer/array types in buffers

Merge pull request #2141 from KhronosGroup/ci-update

Update Ubuntu version in CI.