feat(TestBed): add whitespace handling to compile

Add whitespace handling to the TestBed’s compile function.

Closes #1262. Previously, strings passed with leading or
trailing whitespace would be compiled incorrectly. Now,
valid HTML with arbitrary whitespace in and surrounding it
can be compiled properly.
Checking the rtt is not safe (it could be a child of what you want), I think there is an `.toBeInstanceOf()` that you should rather use (there is also `.toBeA()` but I think the later doesn't work in JS)