[browser][coreCLR] R2R: Produce the WASM interpreter PGO profile package (optimization.browser-wasm.MIBC.Runtime)

Part of #130524. Related: #130517 (interpreter instrumentation), #130518 (JS capture trigger), #130521 (WASM RyuJIT PGO).

## Goal

Turn the WASM interpreter's PGO capability into a maintained **optimization-data package** — a browser-wasm interpreter-startup profile that flows into the CoreLib R2R build the same way the desktop MIBC packages do today.

## Why

The interpreter can produce a block-count profile (#130517) and a developer can capture it from a browser run (#130518). To use that for precompilation in shipping builds, the profile must be collected from a representative workload by CI, packaged, and flowed into the product automatically — not captured by hand.

## Scope

**In:**
- **Collection harness (real browser).** Run a representative **Blazor WASM** workload under headless Chrome (Playwright); arm the capture at startup (`DOTNET_DiagnosticPorts=js://pgo`, interpreter PGO enabled); drive the in-session stop/flush; capture the downloaded `.nettrace`. A real-browser profile is required to represent the Blazor WASM product faithfully (a headless-Node in-process capture is a possible lighter-weight fallback).
- **Convert to `.mibc`.** `dotnet-pgo create-mibc`, referencing the **IL-trimmed** (linked) assemblies whose MVIDs match the trace. ILLink regenerates the module MVID and webcil preserves it, so the untrimmed runtime-pack assemblies will not match — the trimmed `linked` assemblies must be used.
- **Package** as `optimization.browser-wasm.MIBC.Runtime` in the .NET optimization-data pipeline, modeled on the existing non-desktop (Android) MIBC path.
- **Dependency flow.** Flow the package version into the product (VMR → runtime) automatically via the standard optimization-data subscription mechanism.

**Out:** interpreter instrumentation (#130517); the JS trigger (#130518); the runtime-side consumption wiring (separate issue); enabling R2R for the WASM CoreLib.

## Direction / notes

- MIBC is IL-level and **architecture-independent**; the new package adds WASM **interpreter-startup**-specific data, versus the desktop-workload profiles currently reused for browser/wasm by fallback.
- Model the producer on the existing Android MIBC path (a non-desktop RID MIBC package already collected on an emulator), adapting collection to the browser harness and referencing the wasm `linked` (trimmed) assemblies.

## Success criteria

- CI produces a browser-wasm profile and publishes `optimization.browser-wasm.MIBC.Runtime`.
- The package version flows into the product automatically.
- The profile converts and merges via existing tooling with no toolchain changes.

## Open questions

- Harness stability/cost in CI (headless Chrome, download capture).
- Which representative workload(s) best reflect startup hotness for the Blazor WASM product.
- Refresh cadence.
- EventPipe provider/keyword selection for the capture.

> [!NOTE]
> This issue was drafted with GitHub Copilot assistance.