Replace leading/trailing [\s\n\S]* in cts non-multiline regex

We're removing leading and trailing [\s\n\S]* in
assertMatches/assertNotMatches and replacing them with their multiline
variants.

Bug: 121259763
Test: build
Change-Id: If3d71204e066f7874b197fbd32f35321856a1e34
7 files changed