[RyuJIT Wasm] Codegen: Proper `end` placement

[adamperlin]

Wasm requires an end instruction to be placed as a delimiter for the end of an expression. One consequence of this for us in the JIT is that we need to emit an end instruction at the end of codegen for the main portion of a method, as the method body itself is implicitly an expression. In the case of funclets, end will need to be emitted before any funclet code.

Currently, as of #122425, we emit end as part of the epilog generation code if there are no attached funclet blocks. We need to make sure that (at least) the following two cases are handled:

• Emit end even for methods that don't have epilogues
• Emit end to terminate funclets

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[adamperlin]

I believe we've handled all the major cases here, and any others which do come up we can handle as individual bugs.