[ddc,frontend_server] Fix expression compilation after recompile

Update the last known good component after a recompile reject back to
the expected state before the recompile.

Adds tests for expression compilation after recompile accept and
recompile reject cases with `--target=dartdevc`. Similar to existing
tests for the VM.

Removes calls to `_generator.accept()` and
`component.computeCanonicalNames()` from `compileExpressionToJs()`.
These were added very early in the prototype implementation and it is no
longer clear why they would be needed.

Added some additional test cases for expression compilation involving
import resolution because the change that originally added the
`component.computeCanonicalNames()` call implies it was needed for that
reason. See: https://dart-review.googlesource.com/c/sdk/+/138010

TEST=pkg/frontend_server/test/frontend_server_test.dart,pkg/dev_compiler/test/expression_compiler/expression_compiler_test.dart

Change-Id: I9c04bd46e56b33dc654d00fb330de29c3c643a5b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/434522
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>