JIT: don't fall through from a Wasm callfinally across a try_table end

[lewing]

On Wasm, genCallFinally omitted the branch to the callfinally continuation whenever it was the lexically next block. When a try_table interval ends between the BBJ_CALLFINALLYRET and its continuation, codegen emits a validation unreachable after the try_table end, so the fall-through traps at runtime with RuntimeError: unreachable.

This hit ManagedWebSocket.<WaitForServerToCloseConnectionAsync>d__64.MoveNext under browser-wasm R2R. Disassembly showed the normal path calling the finally funclet and then falling into the try_table end, while other paths to the same continuation used call finally; br N.

Changes

• genCallFinally now uses BasicBlock::CanRemoveJumpToTarget, which already refuses fall-through across a Try/ExnRefWrapper end for BBJ_ALWAYS and BBJ_COND (JIT: fix wasm conditional fallthrough #133528). Its assert is widened to accept BBJ_CALLFINALLYRET.
• A DEBUG check in fgWasmControlFlow asserts that every adjacent forward edge that cannot fall through because a Try/ExnRefWrapper ends at its target has an enclosing Block interval, so the explicit branch has a label.
• New regression test JIT/Regression_2/Runtime_134264. The bug needs an async method ending in a user try/catch/finally whose finally is too large to be cloned; a nested try/finally-in-try/catch variant is included.
• Re-enable WebSocketReceiveErrorMessageTests on Wasm R2R.

Validation

• System.Net.WebSockets.Tests, browser-wasm CoreCLR, trimmed R2R on Chrome: before the fix, reproduces the trap; after, 278 run, 0 failed, including the 4 re-enabled tests.
• Runtime_134264 via src/tests/run.sh wasm --runcrossgen2tests (browser): passes with the fix; with the pre-fix JIT it traps with RuntimeError: unreachable in TryCatchFinallyAsync_d__2.MoveNext.
• Checked cross-targeting Wasm JIT: crossgen2 of System.Private.CoreLib and 14 framework assemblies with no asserts. Temporarily disabling block creation for try/catch exits makes the new check fire on both test methods.
• jitformat.py clean.

JIT/Regression_2 is not yet in the curated WASI runtime-test trees; #133265 adds the WASI R2R lane and should include -tree:JIT/Regression_2 to cover this test there.

Resolves #134264

Note

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