[Repo Assist] tests: add GenerativeNestedTypesTests; refactor: use canBindNestedType in ProvidedTypeDefinition; prepare release 8.9.0#508

dsyme merged 2 commits intomasterfsprojects/FSharp.TypeProviders.SDK:masterfrom

repo-assist/tests-nested-types-canBindNestedType-20260423-be3f411fb71826ebfsprojects/FSharp.TypeProviders.SDK:repo-assist/tests-nested-types-canBindNestedType-20260423-be3f411fb71826ebCopy head branch name to clipboard