Allow SCMClient unit tests to set server capabilities.
Review Request #12634 — Created Sept. 24, 2022 and submitted
build_client()can now take default capabilities for the test,
explicitly through a new
caps=argument or through a
default_scmclient_capson the test suite.
This simplifies tests that are sensitive to server capabilities, and
helps entire suites opt into modern behavior by default.
Made use of this in upcoming tests.
Perforce unit tests pass.