[Ide] Excessive `Compilation.Emit` due to Roslyn Compilation churn for C# references

### Description
When C# projects change, Roslyn creates new `Compilation` instances. The F# IDE integration currently uses a `ConditionalWeakTable` to cache the emitted PE reference from these compilations. Because new `Compilation` objects are continually created by Roslyn, the weak table cache misses, causing repeated, expensive metadata-only emissions (`Compilation.Emit(metadataOnly=true)`). This contributes to UI latency and background CPU churn.

### Expected Behavior
We should add a cache based on a stable identifier, such as `(ProjectId, project.Version)`, to avoid re-emitting assemblies unnecessarily when the underlying C# project hasn't functionally changed.

### Actual Behavior
The IDE often experiences excessive background activity because it forces frequent PE emissions for the same actual logic state.

Start by locating the F# IDE integration that uses the ConditionalWeakTable and trace its calls to Compilation.Emit(metadataOnly=true). Compare the cache key with the stable ProjectId and project.Version described in the issue. Done means unchanged C# project state no longer causes repeated metadata-only emissions, while changed versions still refresh the reference.

Written by the indexing model from the issue text.