[TS] Introduce v2 JS abi, with memory allocated by the caller

[coolreader18]

Description of Changes

The main difference from v1 is that syscalls that used to return Uint8Arrays now instead accept ArrayBuffers and write into them. This greatly improves performance, since the module can now reuse buffers when calling into the host, instead of the host allocating anew on every call.

To see the changes from v1 -> v2, you can check the diff between the head of this branch and the "Copy v1.rs to v2.rs" commit.

API and ABI breaking changes

Not sure whether this counts? A new ABI, but we're not breaking the old one.

Expected complexity level and risk

3 - mostly the same as the old one

Testing

No change in behavior, and the typescript package will use the new ABI even though its API isn't changing (yet).

[Centril]

I've added a commit c5c8d0b to extract out common bits between v1 and v2.
Beyond that, I'd like to see documentation for:

• datastore_index_scan_point_bsatn
• datastore_delete_by_index_scan_point_bsatn
• with_arraybuffer_mut
• with_arraybuffer
• JsReturnValue
• procedure_start_mut_tx
• procedure_abort_mut_tx
• procedure_commit_mut_tx

Wherever it applies, I'd also like docs for v1 for the items above.
To the extent you prefer, you can also do this in a follow up.