GraphBuilderTester was introduced at a time where RawMachineAssembler
was going to be deprecated (https://codereview.chromium.org/1423923003/).
Now we know that it's not going to happen any time soon.

Since GraphBuilderTester it's only used in one test which can use
RawMachineAssembler, I updated it and removed the class.

Now the .h file had another class, which is now the only class in the file.
Therefore, I renamed it and updated the include calls to it.

Also updated the include commands: some were not necessary, and some others
could be moved to more aptly places.

Bug: v8:9183
Change-Id: I44bf16090c0515b1b9ff6cbded1bdb0adb4e44e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1594563Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61269}