* fix(build): Include node_modules/@blockly/ in gh-pages branch
- Add node_modules/@blockly to the list of files added to the gh-pages
branch.
- Add a _config.yml file telling Jekyll (which is needed to produce
the homepage served at https://google.github.io/blockly/, and hence
can't be disabled with a .nojekyll file instead) not to exclude
node_modules (which it does by default).
* refactor(build): Modernise git_tasks.js
- Various style updates:
- Use CONSTANT_CASE.
- Use /** JSDoc comments */
- Use `template ${literals}`.
- Use git switch instead of git checkout.
- Try to avoid use of remote names; use URLs where possible.
* refactor(build): Look up upstream git remote
Since git reset can't take a URL but needs an actual remote name,
use git branch -v to look up the remote for
github.com/google/blockly and then use that remote name.
* chores(build): format
