t: introduce WITH_BREAKING_CHANGES prerequisite

t: introduce WITH_BREAKING_CHANGES prerequisite

Earlier c5bc9a7f (Makefile: wire up build option for deprecated
features, 2025-01-22) made an unfortunate decision to introduce the
WITHOUT_BREAKING_CHANGES prerequisite to perform tests that ensure
the historical behaviour that may be different from what we will
have in the future.  It would inevitably invite double-negation when
we need to add tests to ensure the behaviour we want to have in the
future.

Introduce WITH_BREAKING_CHANGES prerequisite and replace the
existing uses of WITHOUT_BREAKING_CHANGES prerequisite.  To catch
any future topics that add more uses of WITHOUT_BREAKING_CHANGES,
mark it as a removed prerequisite.

Signed-off-by: Junio C Hamano <gitster@pobox.com>