feat(wasm): option for initWasm() to return the instance (#3847 #5615)

[Menci]

Description

In Vite's builtin wasm plugin, the exported function initWasm returns the exports property of the WASM instance, which is not always what we want. Some needs the module instance itself (e.g. #3847 #5615).

I added an option getInstance as initWasm's 2-nd parameter. When pass true it will return the instance instead of exports. This is a non-breaking change since omitting the parameter we still get the old behavior.

This PR will close #3847 and close #5615.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

This makes the syntax a bit awkward if we want to get the instance. A couple alternatives I can think of:

1. Introduce ?instance suffix so the wasm function returns the instance
2. Support a __vite_instance property to the first parameter of initWasm()

Otherwise if we do want to introduce a new parameter, making in an object form would be more future-proof.

I'll put this in the next team meeting.

[Menci]

Maybe change to initWasm(imports, { instance: true })?