test: update test dependencies and rearrange files

[erikian]

Just some groundwork related to #1408:

• jest.json has been moved to jest.config.js - that's the default location and makes the test scripts config a little simpler
• updated some Jest- and RTL-related dependencies (including @testing-library/dom from v8 to v9, with no breaking changes that affect us)
• moved the RTL tests from rtl-spec to rtl-spec/components so we can mirror the current structure

[dsanders11]

jest.json has been moved to jest.config.js - that's the default location and makes the test scripts config a little simpler

Let's make this jest.config.ts and get type checking support for the config. The Jest docs have an example using jest.config.ts, and testing it real quick shows it works well without any extra changes - it requires ts-node but I already added that in #1406 when moving other configs to TypeScript.

[dsanders11]

Subjective nit: I'd call this a test: or chore: rather than refactor: since it's not changing code. My personal general rule of thumb is to use test: for changes like this which only touch testing stuff so that I can easily skip over them if tracking down which commit introduced a bug, while refactor: I use for changes which refactor code but shouldn't have user-visible changes.

Minor nit: let's shorten up the title if we can, it's nice when the title is < 72 chars so that the whole message can be seen when scrolling through commit history.

[erikian]

Subjective nit: I'd call this a test: or chore: rather than refactor: since it's not changing code

Yeah, agreed on using test: here 🙂

Minor nit: let's shorten up the title if we can

Done 👍