Name mangling is hard to get right and not easy to read.
This CL replaces the remaining name mangling of types and generics
with simpler names that are not always unique, but then fixes them
up by appending a unique counter.

For struct types, this required an @export annotation since we use some
struct types in CSA.

Drive-by-fixes:

- Overwrite the copy constructor of Type to clear the list
of alias names when creating a new type.

- Change the existing append-a-number scheme to have different
  counters for each name. This the number of changed names when adding
  something and is more readable.

Bug: v8:7793
Change-Id: Ied11ea1a251130f4562ddc0d81967368349e0bf6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1866650
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64449}