reflect: make Value.Type inlineable

reflect: make Value.Type inlineable

This allows the result of Type to be computed much faster.

Performance:

	old     new     delta
	1.76ns  0.66ns  -62.27%

Change-Id: Ie007fd175aaa41b2f67c71fa2a34ab8d292dd0e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/400335
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>