[Dot Shorthands] Rename the static access shorthand feature experiment flag

[kallentu]

@sgrekhov
https://dart-review.googlesource.com/c/sdk/+/407603 fails currently because it's hanging from all the co19 tests using enum-shorthands which is an unknown experiment flag after we rename it to dot-shorthands.

The solution is to make sure the tests use a known experiment. So I'm creating an issue to ask if we could rename all flags in the co19/LanguageFeatures/Static-access-shorthand tests to dot-shorthands and I'll update the DEPS in that PR so we can sync the new flag with the tests using it.

Thanks!

[sgrekhov]

@kallentu the experimental flag in co19 shorthand tests was updated. I've done a roll, but to the commit prior to this one. So, in your CL, change the co19 revision to b14b080, and this update will only contain changes to experimental flags.

[kallentu]

That's perfect, thank you so much @sgrekhov.