Temp - Test branch patch from #2774313 against testbots

This is a temp issue to check a commit from #2774313: Validate library dependencies when extensions are installed and more gracefully deal with library-specific errors at runtime (#16) against the main branch. Queue #2774313 is currently against feature branch "2774313-validate-dependencies" and there appears to be something strange going on with the testbots specific to that branch (tests are not actually being run).

I want to merge the current state of that branch into 8.x-3.x in order to address a main branch test failure, but need to first confirm that the feature branch itself is passing tests. Tests pass fine locally on the current head of "2774313-validate-dependencies" but I'll feel better with a confirmation from the d.o. testbots before doing any more merging.