Fix tail-call handling in interpreter and wasm2c

[keithw]

This PR:

• updates the testsuite, adding new tail-call tests ([test] return_call +indirect with multi-param / multi-result / imported funcs spec#1872) that include imported functions (Fix bug in wasm2c's tail-call optimization code generation #2420 (comment)) and multi-value (Fix bug in wasm2c's tail call optimization codegen #2491 (comment))
• changes the return_call and return_call_indirect .txt files to run the "wasm-3.0" versions of the tests (these are the ones with the changes -- the old "tail-call" proposals directory is not being updated any more)
• fixes an assertion failure in the interpreter that is triggered only when tail-calling a function in the presence of function imports (this bug was partly fixed in interpreter: Fix infinite looping on return_call #1762 and I think this... further fixes it)
• fixes the wasm2c codegen in the presence of imports and multi-param functions

Closes #2491 (fyi @squk)