CI Refactor

[sbillig]

Here's my tentative plan; feedback welcome of course.

• gh action: check and build docs when a PR or push changes a file in docs/

  • b_docs
  • chk_pylint
  • chk_docs_pragma_min_version

• circleci: remove chk_docs_pragma_min_version from workflow

• gh action: run test_antlr_grammar.sh when a file changes in docs/grammar/

• circleci: remove chk_antlr_grammar from workflow (10m small)

• gh action: scripts/run_proofs.sh when a file in test/formal/ changes
  (these are in ci: add github actions for checking docs, antlr grammar, and proofs when files are changed #16135)

• circleci: trigger workflow on run-ci gh label

• gh action: apply run-ci label automatically for org members

• gh action: build and test on ubuntu if any files other than { docs/*, *.md, *.txt } changes (this is the simple workflow that will run by default for non-docs external PRs)

• enable ccache/sccache on solc builds (WIP in CircleCI slimming [WIP] #16125)

We should also consider a less-than-full default workflow for internal PRs. In addition to using fewer circle credits, this will also speed up CI feedback for PRs. I could use some help defining what this should be (if something like this is desirable at all).

Here are the highest-credit jobs in the main workflow, with credit count and cost per job over the past 30 days. Note that the highest monthly usage in the past year was ~5x the past 30 days. Each run of the main workflow costs about $10.30 as it is today, fwiw.