feat!: upgrade to node 18

[sofisl]

This PR:

1. Updates the post-processor image to latest
2. Updates tests to Node 18
3. Importantly: updates the generator to delete any libraries that are no longer maintained. See https://chat.google.com/room/AAAA3k1_t2c/jekVKt62rc0
4. Updates all dependencies to their latest version, including gaxios and nodejs-googleapis-common (see feat!: Support AIP-193 for GaxiosError gaxios#699, fix: Ensure Marshalled GaxiosResponse has all properties nodejs-googleapis-common#605), which were caught in these tests
5. Updates all instances of GaxiosPromise to Promise (chore!: bump deps nodejs-googleapis-common#591)
6. Reruns the generator to update all of the APIs with the new syntax.

BEGIN_COMMIT_OVERRIDE
feat!: upgrade to node 18
END_COMMIT_OVERRIDE

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• .kokoro/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/lint.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/samples-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/system-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/samples-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/system-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs-devsite.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/samples-test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/system-test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/test.bat - .kokoro files are templated and should be updated in synthtool
• .kokoro/test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/trampoline_v2.sh - .kokoro files are templated and should be updated in synthtool
• .github/workflows/ci.yaml - .github/workflows/ci.yaml (GitHub Actions) should be updated in synthtool

[sofisl]

The last fields aren't updating in the generator because they're not present in index.json. Looking.