Add code formatter and auto-format existing code

[jake-low]

The diff on this PR is huge, but you can ignore everything under src/ (it's all auto-formatting).

What this PR does:

• adds Biome as a dependency. Biome is a new code formatter and linter for JavaScript (and also TypeScript, CSS, SCSS). Its formatting output is identical to Prettier, but it's >30x faster. It is also a very capable linter (and much faster than ESLint). I plan to replace our usage of ESLint with Biome's linter in a future PR.
• formats all existing code with Biome
• sorts all imports with Biome (this is a separate step in Biome; I ran it as a one-off operation for now but will probably add it to CI too in the future)
• adds a .git-blame-ignore-revs file to record "uninteresting" commits that should be excluded from git blame output, both locally and on Github. Github uses this file automatically; see the comment in the file for how to configure git to do the same locally.
• adds a new yarn run format command which runs Biome on all source code and formats it
• adds a new yarn run check command which checks that code is correctly formatted (using Biome) and that there are no lint errors (using ESLint), but does not modify any code
• adds an optional git hook to run these checks each time you git commit. There are instructions in DEVELOPMENT.md for setting this up for your development environment.
• runs the checks in CI to make sure PRs don't introduce new linting or formatting issues