Add strict_extension option for SPIR-V frontend

[davnotdev]

Is your feature request related to a problem? Please describe.
I am trying to convert a SPIR-V shader that uses a dynamic sampler array to wgsl.
However, the OpExtension "SPV_EXT_descriptor_indexing" instruction is not supported.

Describe the solution you'd like
There could be a flag similar to strict_capabilities called strict_extensions which could throw a warning for unsupported extensions. Or there could be some other flag to only allow certain extensions.

Describe alternatives you've considered
My currently solution is to remove the SPV_EXT_descriptor_indexing extension. Although this new shader does succeed when passed through naga, it does not pass spirv-val.

The disassembly of the shader in question

[davnotdev]

strict_extension would imply that by default, ALL extensions would pass whether they are supported or not. Perhaps something like allow_all_extensions would be less confusing?