This updates BazaarClient to add formal support for dependency checks.

BazaarClient.check_dependencies() now determines if Breezy or Bazaar

is installed, and sets appropriate flags for the tool to use.
The bzr and is_breezy attributes have become properties, which will

trigger a dependency check if one is not performed. Similarly,

get_local_path() will also perform a dependency check if needed. This

is all in case of legacy usage where these are accessed before calling

setup() or has_dependencies(). In RBTools 5, these will instead

raise an exception.
Unit tests have been updated to include new dependency-related tests.

They also now leverage the dependency checks, rather than duplicating

checks or working around the different names of the tool. Tests that

require a working client will be skipped if missing a dependency.

Unit tests pass on Python 3.7 through 3.11.
Tested with Breezy installed, with Bazaar installed, and with neither

installed.