feat: add an alwaysInline builtin

[CountBleck]

Changes proposed in this pull request:
⯈ Add an alwaysInline builtin that inlines any inner function calls

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[CountBleck]

@JairusSW let me know if anything else is desired for this builtin

[HerrCai0907]

what is the difference between inline and this builtin?

[CountBleck]

@HerrCai0907 this gives you fine-grained control over when a function is inlined (by specifying it in the relevant call sites, instead of in the definition).

@JairusSW has an example as to how this would be useful in as-json.

[JairusSW]

@CountBleck would it be possible to just rename it to inline()

[CountBleck]

@CountBleck would it be possible to just rename it to inline()

I originally intended to name it inline, but I didn't want there to be a conflict with the @inline decorator in the TypeScript typings.

[HerrCai0907]

LGTM for implement part.
But I have some concern about design. I think we should avoid to pollute global scope. load / store / call_indirect can be mapped to low level wasm instruction directly so we keep them in global scope. But for alwaysInline and unchecked, I think we should place them in a special namespace or start with some special prefix.

For C++, std library used compiler-implemented function will start with __. some builtin function will start with __builtin. I wonder should we also do something like this?

e.g.
use this like

builtin_opt.unchecked(....)
builtin_opt.alwaysInline(....);

[CountBleck]

Sounds like a good idea, but I'm hesitant to rename/move unchecked since that would be a breaking change.

[HerrCai0907]

Sounds like a good idea, but I'm hesitant to rename/move unchecked since that would be a breaking change.

At least we can start from alwaysInline

[MaxGraey]

Sounds like a good idea, but I'm hesitant to rename/move unchecked since that would be a breaking change.

How about to use inlined(fn(...)) instead of alwaysInline(fn(...)). It's shorter and consistent with unchecked

[CountBleck]

I'll do that. What do you think about a namespace for inlined/unchecked? We can alias export const unchecked = builtin_opt.unchecked; (or whatever the namespace would be called).