[internal] Don't download Go third-party dependencies multiple times (Cherry-pick of #13352)

[Eric-Arellano]

Turns out that #13339 didn't actually work - we are redownloading the same modules several times with Go! Downloads happen when:

1. determining GoModInfo (once per go.mod)
2. AllDownloadedModules (once per go.mod)
3. Determining metadata for each third-party package (once per third-party module)
4. Determining metadata for each first-party package (once per first-party package/directory)

This PR fixes it so that we only download modules a single time, once per go.mod.

To fix this, we stop treating third-party modules like first-party modules, i.e. we stop cd-ing into its downloaded directory and running go list directly in it, using its own go.mod and go.sum. That requires that the chroot has all of the module's transitive dependencies present, and it also resulted in issues like #13138. Instead, the much simpler thing to do is run go list '...' to do all third-party analysis in a single swoop. That gets us all the analysis we need.

We also extract the relevant .go files from all of the downloaded GOPATH, i.e. all the downloaded modules. For compilation, all we need is the .go files + the metadata we had earlier calculated. Compilation doesn't need access to anything else like other package's.

For first-party analysis, we copy the whole GOPATH into the chroot. (This is really slow! We need something like #12716 to fix this.)

Benchmark

Running in https://github.com/toolchainlabs/remote-api-tools.

Before:

❯ hyperfine -r 5 './pants_from_sources --no-process-execution-local-cache --no-pantsd package ::'
  Time (mean ± σ):     36.467 s ±  0.603 s    [User: 41.109 s, System: 38.095 s]
  Range (min … max):   35.518 s … 37.137 s    5 runs

Fixing only third-party analysis:

❯ hyperfine -r 5 --show-output './pants_from_sources --no-process-execution-local-cache --no-pantsd package ::'
  Time (mean ± σ):     29.880 s ±  0.901 s    [User: 29.564 s, System: 15.281 s]
  Range (min … max):   28.835 s … 31.312 s    5 runs

Fixing everything:

❯ hyperfine -r 5 './pants_from_sources --no-process-execution-local-cache --no-pantsd package ::'
  Time (mean ± σ):     26.633 s ±  2.283 s    [User: 24.115 s, System: 30.453 s]
  Range (min … max):   24.570 s … 30.037 s    5 runs

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