* Start logger in startProgress to avoid assertion failure

There are lots of places that create a Status() and all but two of them call ..start() immediately. This is one of the places that doesn't, which causes an assertion failure when running with --enable-asserts and the other is in the same file (I suspect it's also incorrect, but possibly it's never used - I'll look at that separately when I can trace some code that calls it).

Fixes #20812.

* Enable asserts for tools tests

* Fix lint

* Rename enableAsserts -> enableFlutterToolAsserts

To make it clearer that it only enables asserts for flutter_tools when set.