bazel: speed up `dev gen bazel`

This is a tracking issue for speeding up `dev gen bazel`. This can include unconditional speedups and optimizations in addition to conditional ones, since `dev gen bazel` is conditional in general.

## "collapse" binaries

`bazel-generate.sh` is made up of many distinct steps which we split into 3 categories:

1. Pre-`gazelle`
2. `gazelle`
3. Post-`gazelle`

There are 5 distinct post-`gazelle` build steps:

```
generate-logictest
generate-acceptance-tests
generate-distdir
genbzl
generate-bazel-extra
```

Just running `bazel run` 5 times is already quite slow, even for a no-op binary. It would be best to "collapse" these, to whatever extent possible, into only one binary, and therefore only one `bazel run`.

Having said that, some of these binaries have more dependencies than others (specifically `generate-logictest`). Keeping it separate may therefore be beneficial.

See also #123164

Epic: CRDB-17171

Jira issue: CRDB-38219