Prepare 2.16.0.dev3

[stuhood]

Internal

• Get rid of _ToolLockfileMixin. (#17823)

• Fix build-support/bin/deploy_to_s3.py. (#17818)

• Upgrade setproctitle to 1.3.2 (#17804)

• Document the release tag back-fill script. (#17808)

• Add a release tag backfill script. (#17806)

• Set up release tag mapping workflow. (#17801)

• go: fix path lookup for copied header files (#17798)

• go: set replace_sandbox_root_in_args=True since replacement is used (#17797)

• go: set missing Goal.environment_behavior on a debug goal (#17799)

• go: rename option to --go-test-coverage-packages (#17795)

• A stub page for dep validation docs. (#17788)

• Upgrade to newest remote execution proto (#17786)

• Adding tests for cc dependency inference showing source roots as include_directories (#17738)

• Fix validation of release PEXes. (#17785)

• Unconditionally register export-codegen goal in pants.core (#17782)

• go: allow exporting cgo codegen for third party packages (#17770)

• Properly set pex_root when running python sources in-sandbox. (#17750)

• Renames output_files and output_directories fields for experimental_shell_command (#17744)

[stuhood]

The first commit is #17830.