[TEST] Beef up InternalEngineTest and remove bogus timeouts
Ban java.io.File in tests.

Restrict use of java.io.File to 5 methods (excluded), but otherwise ban.
This is a prerequisite to do any mocking here.

I don't try to do any heavy cleanup on these tests, I am not familiar with them.
So this is mostly a rote straightforward conversion.

Closes #8836
Docs: Update repositories.asciidoc

1. Enable the repository using "add-apt-repository" to avoid this error "No command 'deb' found".
2. Adding "sudo" to update and install command.

Closes #8691
Docs: Fix the wording for inner hits a bit

Closes #8747
[TEST] compare strings and strings - leftover from Path API refactoring
[TEST] LoggingListener to restore the initial logger levels after any modification

Modifications to LoggingListener pushed with #8820 caused the original logger levels not to be reset after modifications, as the new state was saved for restore instead of the previous one.

 Added unit tests for LoggingListener as well.

Closes #8845
[TEST] Restore test logging level after test is done
Core: also log byte size and doc count when we log slow merges

Closes #8855

Closes #8853