[internal] Generate _go_internal_package targets

[Eric-Arellano]

Closes #13049. This greatly reduces boilerplate and also allows us to make some fields required like import_path and subpath, so that we don't have to calculate those in consuming rules like build_go_pkg.py.

The address format

The generated address looks like project#./dir. @tdyas offered that this is intuitive for Go developers because they have to say go build ./dir already with the leading ./.

This solves how to represent when the _go_internal_package is in the same dir as the go_mod: project#./.

This also makes very clear the difference from external packages like project#rsc.io/quote vs. internal packages like project#./dir.

Improves dependency inference

Now that the import_path field is required for both _go_internal_package and _go_external_package, we can create a global mapping of import_path -> pkg_target. This is necessary for #13114.

This also improves performance. We don't need to call ResolvedGoPackage on all the candidate targets a package might depend on to calculate their import paths. We do still need it when resolving the deps of a particular _go_internal_package, but we can be lazier when we call that codepath in not evaluating all candidate targets.

dependencies benchmark

As expected, there is no difference because we are finding the dependencies of everything, so we still have to call ResolvedGoPackage. The perf gains are only in things sometimes being less eager, which isn't the case here.

Before:

❯ hyperfine -r 5 './pants_from_sources --no-pantsd --no-process-execution-local-cache dependencies ::'
  Time (mean ± σ):     26.501 s ±  1.537 s    [User: 29.554 s, System: 24.115 s]
  Range (min … max):   24.928 s … 28.763 s    5 runs

After:

❯ hyperfine -r 5 './pants_from_sources --no-pantsd --no-process-execution-local-cache dependencies ::'
  Time (mean ± σ):     26.359 s ±  0.526 s    [User: 29.600 s, System: 23.769 s]
  Range (min … max):   25.625 s … 26.993 s    5 runs

package benchmark

Before:

❯ hyperfine -r 5 './pants_from_sources --no-pantsd --no-process-execution-local-cache package ::'
  Time (mean ± σ):     33.777 s ±  0.248 s    [User: 39.221 s, System: 39.389 s]
  Range (min … max):   33.517 s … 34.062 s    5 runs

After:

❯ hyperfine -r 5 './pants_from_sources --no-pantsd --no-process-execution-local-cache package ::'
Benchmark #1: ./pants_from_sources --no-pantsd --no-process-execution-local-cache package ::
  Time (mean ± σ):     31.049 s ±  0.702 s    [User: 40.606 s, System: 40.537 s]
  Range (min … max):   30.512 s … 32.273 s    5 runs

TODO: fix go_binary inference of main field

#13117 added inference of the main field for go_binary, that it defaults to the go_package defined in that directory.

But target generation no longer generates targets actually in each directory. All generated targets are "located" in the BUILD file of the go_mod, i.e. their spec_path is set to that. So it no longer looks to AddressSpecs like there are any targets in each subdirectory, and there are >1 _go_internal_package targets in the go_mod dir.

Instead, we should use the subpath field to determine what directory the targets correspond to.

[ci skip-rust]
[ci skip-build-wheels]

[tdyas]

FYI This may need to say go mod download all. See #13136. But fix in a separate PR in any event.

[Eric-Arellano]

Performance benchmarks posted. A 2 second speedup for ./pants package ::. I'll take it!