wasmparser: Missing options in WasmFeatures

[Robbepop]

Currently the WasmFeatures struct in the wasmparser crate has many options for controlling single Wasm proposal implementations.
However, some Wasm proposals such as nontrapping-float-to-int-instructions, sign-extension-ops and mutable-global are missing from there.

Is this intentional? If yes, what is the reason?

If not, would the authors of the wasmparser crate like to receive PRs to add those configuration options so that wasmparser can be used to validate against Wasm inputs making use of those features?

Motivation

For some use cases it might be very important to guard against usage of certain unsupported Wasm proposals. An example for this is in the context where Wasm instructions are metered and there is no defined metering for certain instructions of Wasm proposals.

ToDo

• Add mutable_global: bool field to WasmFeatures to enable or disable the mutable-global Wasm proposal.
• Add nontrapping_float_to_int_instructions: bool field to WasmFeatures to enable or disable the nontrapping-float-to-int-instructions Wasm proposal.
• Add sign_extension_ops: bool field to WasmFeatures to enable or disable the sign-extension-ops Wasm proposal.

[alexcrichton]

I think this is mostly because those proposals were largely stable before they were added here, but it should be fine to retroactively add them if necessary.

[Robbepop]

Okay, I added some TODOs to the initial comment and am looking to tackle this soon.