go/types: turn TestBenchmark into a normal benchmark
go/types: turn TestBenchmark into a normal benchmark

TestBenchmark doesn't use the -bench flag, so that it can format custom
output -- the number of checked lines per second. This is a barrier both
to discoverability, and to piping benchmark output into analysis tools
such as benchstat.

Using testing.B.ReportMetric and a bit of manual timing, we can achieve
similar results while conforming to normal benchmark output. Do this,
and rename the test func to BenchmarkCheck (for symmetry with
TestCheck).

Change-Id: Ie8f2259c1ca9e6986f0137287acf8eb2843f96b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/257958
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Trust: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

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