Ux should disable function invocation button until host is fully initialized

Opening tracking item in this repo as a follow up from CRI investigation.

Test/Run button on portal should be disabled until Host is fully initialized - in case of out-of-proc languages - this also means host and language worker process should be ready.

If this information is not surfaced already, host should provide an API that UX can call into to figure out when to enable Run button

cc @fabiocav @soninaren @ehamai @ConnorMcMahon

No source files or tests are named. Start by tracing how host initialization state is exposed and how the portal decides whether the Test/Run button is enabled, including host and language-worker readiness for out-of-process languages. Done means the button remains disabled until initialization is complete and the required readiness information is available to the UX.

Written by the indexing model from the issue text.