[browser][coreCLR] R2R: Consume the WASM PGO profile in the CoreLib R2R build #132717

Part of #130524. Related: #130517, #130521. Depends on the profile-production issue (the optimization.browser-wasm.MIBC.Runtime package).

Goal

Wire the browser-wasm interpreter PGO profile into the WASM CoreLib R2R optimization-data merge, so precompilation uses the interpreter-collected startup hotness.

Why

Once the profile package exists (separate production issue) and WASM CoreLib R2R is enabled (already in progress on a separate branch), the profile still has to be restored and merged into the optimization data the R2R build consumes. Today browser/wasm has no dedicated profile — it falls back to desktop (linux-x64) profiles.

Scope (runtime-side wiring only)

In:

• Add the optimization.browser-wasm.MIBC.Runtime dependency (eng/Version.Details.xml) + version property (eng/Versions.props).
• Add a MibcArchitecture="browser/wasm" entry (+ PackageDownload) in eng/restore/optimizationData.targets, so the package restores into artifacts/mibc/browser/wasm/data/ and is merged into StandardOptimizationData.mibc by src/coreclr/crossgen-corelib.proj's existing merge target.
• Guard with Condition="Exists(...)" so it's a no-op until the package is available.

Out:

• Producing the package (separate production issue).
• Enabling R2R for the WASM CoreLib — already in progress on a separate branch. This issue only ensures the WASM profile flows into that merge.

Notes

• MIBC is architecture-independent; this replaces the desktop-profile fallback for browser/wasm with WASM interpreter-startup-specific data.
• Do not commit ad-hoc/sample-derived .mibc as optimization data — the profile comes from the package.

Success criteria

• With the package present, the WASM CoreLib R2R build consumes the merged StandardOptimizationData.mibc including the browser-wasm data, with no changes to the precompilation toolchain.

Open questions

• Confirm crossgen2 accepts interpreter-produced, IL-offset-keyed counts unchanged and selects the expected hot methods (relates to the open question in [browser][coreCLR] R2R: Interpreter PGO instrumentation (block counts) #130517).