internal/abi: refactor (basic) type struct into one definition

internal/abi: refactor (basic) type struct into one definition

This touches a lot of files, which is bad, but it is also good,
since there's N copies of this information commoned into 1.

The new files in internal/abi are copied from the end of the stack;
ultimately this will all end up being used.

Change-Id: Ia252c0055aaa72ca569411ef9f9e96e3d610889e
Reviewed-on: https://go-review.googlesource.com/c/go/+/462995
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>