[Wasm/RyuJit] treat all try side-entries as try entries for throw helpers

[AndyAyersMS]

For Wasm DFS in graphs where try regions may have side entries (async), ensure the DFS will always eagerly visit (and hence first retreat from) any throw helper blocks in the region, no matter which entry is visited first by DFS.

This ensures the throw helper ends up last in the RPO and hence is reachable by a forward branch from anywhere in the region.

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[Copilot]

Pull request overview

Adjusts Wasm-specific DFS successor enumeration so throw-helper (ACD) blocks are treated as successors not only from try headers, but also from “side-entry” blocks into a try region (e.g., async/catch resumption targets). This helps ensure throw helpers are visited early in DFS and end up late in RPO, enabling forward-branch reachability within the region.

Changes:

• Introduces a local predicate to classify “generalized try entries” (try header or side-entry).
• Uses this predicate when injecting ACD throw-helper successors during Wasm successor enumeration.

[AndyAyersMS]

Fixes this error where the throw helper ends up earlier in wasm ordering than one of its targets:

Assertion failed '!"Can't find target in control stack"'
in 'System.CodeDom.Compiler.IndentedTextWriter.OutputTabsAsync' during 'Generate code'

Note we don't generally have flow edges to throw helpers.

@jakobbotsch PTAL
fyi @dotnet/jit-contrib