Reduce # of resolves when packaging pex_binary and python_awslambda targets

[Eric-Arellano]

We already use repository PEXes when [python-setup].resolve_all_constraints or experimental lockfile are set, thanks to code in pex_from_targets.py. Those benefit from using the same repository PEX as the rest of the codebase, e.g. when using MyPy or Pytest.

However, we were ignoring this repository pex with python_awslambda and pex_binary and resolving more granular repository PEXes after having already resolved the global one. Iiuc, those more granular ones are not coming from the global one. This is wasted work.

While a TwoStepPex could be useful in those two callsites if you are not using constraints/lockfiles, we strongly encourage using lockfiles.

Removing TwoStepPex allows us to remove complexity in a hairy part of the codebase, especially as we add new complexity for lockfile support.

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

[Eric-Arellano]

I think we may actually want to cherry-pick this to 2.6.x? It looks like this is resulting in more work than necessary, like we were setting up multiple repository PEXes (which is how the code reads to me). Compare before:

❯ ./pants package build-support/bin::
There is no pantsd metadata at /Users/eric/code/pants/.pids/48089be3df2a/pantsd.
18:50:08.87 [INFO] Initializing scheduler...
18:50:09.82 [INFO] Scheduler initialized.
18:50:12.07 [INFO] Completed: Building build-support.bin/deploy_to_s3.pex
18:50:12.12 [INFO] Completed: Building build-support.bin/check_inits.pex
18:50:12.14 [INFO] Completed: Building build-support.bin/check_banned_imports.pex
18:50:12.70 [INFO] Completed: Resolving 2 requirements: ansicolors==1.1.8, typing-extensions==3.7.4.3
18:50:12.81 [INFO] Completed: Resolving 1 requirement: packaging==20.9
18:50:13.24 [INFO] Completed: Resolving 4 requirements: ansicolors==1.1.8, requests[security]>=2.25.1, types-requests==2.25.0, typing-extensions==3.7.4.3
18:50:13.29 [INFO] Completed: Building build-support.bin/reversion.pex with 2 requirements: ansicolors==1.1.8, typing-extensions==3.7.4.3
18:50:13.39 [INFO] Completed: Building build-support.bin/changelog.pex with 1 requirement: packaging==20.9
18:50:13.82 [INFO] Completed: Building build-support.bin/release_helper.pex with 4 requirements: ansicolors==1.1.8, requests[security]>=2.25.1, types-requests==2.25.0, typing-extensions==3.7.4.3
18:50:15.85 [INFO] Completed: Resolving 4 requirements: PyYAML<5.5,>=5.4, toml==0.10.2, types-PyYAML==5.4.3, types-toml==0.1.3
18:50:16.23 [INFO] Completed: Building build-support.bin/generate_github_workflows.pex with 4 requirements: PyYAML<5.5,>=5.4, toml==0.10.2, types-PyYAML==5.4.3, types-toml==0.1.3
18:50:18.12 [INFO] Completed: Resolving 12 requirements: PyYAML<5.5,>=5.4, ansicolors==1.1.8, packaging==20.9, psutil==5.8.0, pystache==0.5.4, requests[security]>=2.25.1, setproctitle==1.2.2, toml==0.10.2, types-PyYAML==5.4.3, typ... (66 characters truncated)
18:50:19.28 [INFO] Completed: Building build-support.bin/generate_docs.pex with 12 requirements: PyYAML<5.5,>=5.4, ansicolors==1.1.8, packaging==20.9, psutil==5.8.0, pystache==0.5.4, requests[security]>=2.25.1, setproctitle==1.2.2... (106 characters truncated)
18:50:19.29 [INFO] Wrote dist/build-support.bin/changelog.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/check_banned_imports.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/check_inits.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/deploy_to_s3.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/generate_docs.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/generate_github_workflows.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/release_helper.pex
18:50:19.29 [INFO] Wrote dist/build-support.bin/reversion.pex

After:

❯ ./pants package build-support/bin::
There is no pantsd metadata at /Users/eric/code/pants/.pids/48089be3df2a/pantsd.
18:49:06.73 [INFO] Initializing scheduler...
18:49:07.74 [INFO] Scheduler initialized.
18:49:21.49 [INFO] Completed: Resolving 3rdparty/python/lockfile.txt
18:49:22.42 [INFO] Completed: Building build-support.bin/deploy_to_s3.pex
18:49:22.42 [INFO] Completed: Building build-support.bin/check_banned_imports.pex
18:49:22.45 [INFO] Completed: Building build-support.bin/changelog.pex with 1 requirement: packaging==20.9
18:49:22.45 [INFO] Completed: Building build-support.bin/check_inits.pex
18:49:22.46 [INFO] Completed: Building build-support.bin/generate_github_workflows.pex with 4 requirements: PyYAML<5.5,>=5.4, toml==0.10.2, types-PyYAML==5.4.3, types-toml==0.1.3
18:49:22.46 [INFO] Completed: Building build-support.bin/reversion.pex with 2 requirements: ansicolors==1.1.8, typing-extensions==3.7.4.3
18:49:22.81 [INFO] Completed: Building build-support.bin/release_helper.pex with 4 requirements: ansicolors==1.1.8, requests[security]>=2.25.1, types-requests==2.25.0, typing-extensions==3.7.4.3
18:49:23.53 [INFO] Completed: Building build-support.bin/generate_docs.pex with 12 requirements: PyYAML<5.5,>=5.4, ansicolors==1.1.8, packaging==20.9, psutil==5.8.0, pystache==0.5.4, requests[security]>=2.25.1, setproctitle==1.2.2... (106 characters truncated)
18:49:23.54 [INFO] Wrote dist/build-support.bin/changelog.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/check_banned_imports.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/check_inits.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/deploy_to_s3.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/generate_docs.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/generate_github_workflows.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/release_helper.pex
18:49:23.54 [INFO] Wrote dist/build-support.bin/reversion.pex