wasm2c: allow embedder to configure elimination of dead OOB reads

[shravanrn]

This PR also allows the embedder to disable force_reads (this is off by default, since it is non conforming), as it speeds up several sandboxing workloads by a large amount

• Sandboxed XML parsing with libExpat by 5%
• Sandboxed Audio speed adjustment with libSoundTouch by 10%

While the force read preserves Wasm's determinism guarantees, it clearly comes at a large cost. This cost is not worth for embedders that care only about security and not the determinism guarantees. These are both libraries that Firefox currently sandboxes, and thus this is a feature that I definitely want to land and use.

wasm2c would not be the first compiler to add the option for this feature. Currently Wamr and aWsm enable this by default and don't have a way to disable it, while Wasmer enables it by default and has a switch to disable it. I think wasm2c should remain conformant and not go that far, but it can provide an off-by-default option for this.

Additionally, the actual feature is only about 5 lines so is easy enough to maintain.

[shravanrn]

@sbc100 I have split out the change as requested. As noted above, this is a change I definitely want to land and use soon due to the performance implications.