[analyzer] Refactor const evaluator visitBinaryExpression and tests.

Made more of the tests consistent in `evaluation_test` (slowly, but surely).

Change-Id: I515c4d6d81cedcc1d8d20080e231ac1e0afb5ec7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/312200
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

Author: kallentu