Added --clearWatchOutput flag

[JoshuaKGoldberg]

Makes the 2.7 behavior of clearing the console on recompiles opt-in.

Description: "Whether to clear the console in watch mode on new results."
Since the pretty? compiler options flag is marked as @internal, made this one too.

Sibling PR to #21303. IMO this is a better fix, as the added behavior of clearing the console has proven itself troublesome.

Fixes #21295.

[JoshuaKGoldberg]

16:14:16   59316 passing (2m)
16:14:16   1 failing
16:14:16 
16:14:16   1) conformance tests
16:14:16        conformance tests for tests/cases/conformance/types/uniqueSymbol/uniqueSymbolsErrors.ts
16:14:16          Correct errors for tests/cases/conformance/types/uniqueSymbol/uniqueSymbolsErrors.ts:
16:14:16      Error: The baseline file uniqueSymbolsErrors.errors.txt has changed.

Does not show up locally and does not relate to this change. Unrelated?

[weswigham]

#22247 fixes the build break

[mhegazy]

#21303 is merged now, I do not think we want to change the default yet again.