* add GL_EXT_texture_shadow_lod feature detection
* allow more cases of cube depth texture sampling in glsl
* add test for sampling a cubemap array depth texture with lod
* add test for chosing GL_EXT_texture_shadow_lod over the grad workaround if instructed
* add changelog entry for GL_EXT_texture_shadow_lod
* fix criteria for requiring and using TEXTURE_SHADOW_LOD
* require gles 320 for textureSampling over cubeArrayShadow
* prevent false positives in TEXTURE_SHADOW_LOD in checks
* make workaround_lod_with_grad usecase selection less context dependant
* move 3d array texture error into the validator
* correct ImageSample logic errors
Following Rust convention, let `naga::front::wgsl::ParseError`'s
methods `emit_to_stderr_with_path` and `emit_to_string_with_path`
accept any `AsRef<Path>` argument as the path.
Pass input paths in snapshot tests, so that failures processing
shaders name the input file being processed.
