Implement basic nested language detection support #1801

Job	Run time
Build on windows-latest for repo global.json	23m 23s
Build on windows-latest for 6.0 stable	23m 18s
Build on windows-latest for 7.0 preview	27m 9s
Build on macos-latest for repo global.json	30m 15s
Build on macos-latest for 6.0 stable	28m 38s
Build on macos-latest for 7.0 preview	30m 15s
Build on ubuntu-latest for repo global.json	18m 54s
Build on ubuntu-latest for 6.0 stable	19m 44s
Build on ubuntu-latest for 7.0 preview	19m 45s
	3h 41m 21s

Provide feedback