Use treemacs for metals icon. #237

Job	Run time
build (ubuntu-latest, 27.2, false)	1m 34s
build (ubuntu-latest, 28.2, false)	1m 47s
build (ubuntu-latest, 29.1, false)	1m 30s
build (macos-latest, 27.2, false)	3m 25s
build (macos-latest, 28.2, false)	3m 46s
build (macos-latest, 29.1, false)	3m 42s
build (windows-latest, 27.2, false)	2m 27s
build (windows-latest, 28.2, false)	2m 10s
build (windows-latest, 29.1, false)	2m 3s
build (ubuntu-latest, snapshot, true)	1m 50s
build (macos-latest, snapshot, true)	7m 15s
build (windows-latest, snapshot, true)	1m 4s
	32m 33s

Provide feedback