This cleans up the ci scripts so that they can be run from an arbitrary directory, and so that they don't have any bash lint issues, and are more explicit about which dart/pub/dartanalyzer executable they run.
I also fixed the format script to take a "--fix" argument that will fix all of the formatting issues found, including trailing whitespace and gn files.
I added a warning to the license script about untracked/ignored files in the fluttter repo because those so often trip up the license script.
I added missing license information to the ci scripts too.
There's now a bit of boilerplate at the beginning of each script (the follow_links function) in order to reliably find the actual location of the script: I'd put it into a common file, except that that code would be needed to reliably find the common location too, so I needed to duplicate it. It's the same boilerplate as what is used in the flutter/flutter repo for the flutter and dart scripts.
I deleted the ci/test.sh script, since it seems to be obsolete (the test it tries to run doesn't exist anywhere).
This replaces `ci/test.sh` with `run_tests.sh`. `run_tests.sh` includes
`ci/test.sh` and multiple other tests.
Partially addresses flutter/flutter#22682. Temporarily skipped tests
should be fixed and re-enabled in a follow-up commit.
