go/types, types2: flip on position tracing

go/types, types2: flip on position tracing

Running compilebench with flags off / on, we get the below:

                         │   old.txt    │              new.txt               │
                         │    sec/op    │   sec/op     vs base               │
Template                    149.2m ± 6%   155.5m ± 5%       ~ (p=0.280 n=10)
Unicode                     110.1m ± 3%   105.8m ± 7%       ~ (p=0.280 n=10)
GoTypes                     774.0m ± 6%   757.7m ± 2%       ~ (p=0.247 n=10)
Compiler                    109.6m ± 6%   109.8m ± 6%       ~ (p=0.579 n=10)
SSA                          4.562 ± 2%    4.550 ± 2%       ~ (p=0.436 n=10)
Flate                      101.65m ± 9%   96.32m ± 7%  -5.24% (p=0.043 n=10)
GoParser                    168.7m ± 6%   173.7m ± 6%       ~ (p=0.436 n=10)
Reflect                     390.2m ± 5%   387.8m ± 6%       ~ (p=0.684 n=10)
Tar                         185.9m ± 3%   182.2m ± 4%       ~ (p=0.529 n=10)
XML                         212.7m ± 4%   211.4m ± 4%       ~ (p=0.971 n=10)
LinkCompiler                490.9m ± 4%   480.4m ± 4%       ~ (p=0.353 n=10)
ExternalLinkCompiler         1.501 ± 1%    1.501 ± 1%       ~ (p=0.853 n=10)
LinkWithoutDebugCompiler    311.8m ± 4%   308.6m ± 4%       ~ (p=0.579 n=10)
StdCmd                       17.60 ± 1%    17.62 ± 1%       ~ (p=0.912 n=10)
geomean                     427.5m        424.2m       -0.77%

Overall, we do not see a statistically significant perforance impact. Flate
actually reports a speedup, but with a p-value of 0.043, it's quite close
to the significance threshold (which is fairly lenient). In my opinion,
this is likely due to chance.

Fixes #51603

Change-Id: I7f439730be45e02c7f799df768590ef78e321952
Reviewed-on: https://go-review.googlesource.com/c/go/+/676816
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>