go/types: add the TypeParam.Obj method
go/types: add the TypeParam.Obj method

Users should be able to access the type name associated with a type
parameter.

Change-Id: I495c3b4377f9d4807b1e78ad341e573d4d3c7bff
Reviewed-on: https://go-review.googlesource.com/c/go/+/343931
Trust: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

golang/go,golang/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,golang/go