Fix some issues in the new relevance computations

The code to check the element kind was not being used in a few places
because (a) the generator wasn't always generating a table when it
should and (b) the key for the table wasn't always being set when
creating the OpType. Both of these issues have been mostly addressed.

That required re-generating the element kind tables.

There were several places where context type information wasn't being
used when building suggestions. This has been fixed for all the places
I'm currently aware of.

There were a couple of places where the context type wasn't being
computed where it could have been. I have fixed the places I'm aware of.

Context types were not being computed anywhere because of a bug that
has now been fixed.

There is now one place that computes and caches the context type, which
should improve performance slightly.

I also removed some dead code that I discovered in the process of making
the other changes and cleaned up a couple of places in the code that
were suboptimal.

Change-Id: Ieae8dcc71b986841be3078d6e0b3a653c35384b8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/148237
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>