fix(ExplicitVariability): change many Flat_hash_map container into Bt… #1100

Job	Run time
test / prepare / prepare	32s
test / tidy	4s
test / test-repository / test-linux-python / linux-python (3.12)	4s
test / semantic-commit / semantic-commit	4s
test / test-repository / test-windows-python / windows-python (3.12)	5s
test / test-repository / test-linux / setup-linux-systems	3s
test / test-repository / test-windows / windows	5s
test / test-repository / test-linux / linux	1s
test / release	0s
test / deploy-repository	0s
	58s

Provide feedback