cmd/compile/internal/types2: rename TypeParams to TParamList

The 'TypeParams' name is too easily confused with the singular
'TypeParam', and does not say anything about what type of collection it
is. We decided that TTuple was not great. TParamList seems OK for now,
though perhaps a better name will emerge.

Change-Id: I5eabdc91b1f666bb4c7ea8acdbebf7c372d19227
Reviewed-on: https://go-review.googlesource.com/c/go/+/341861


Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>