tests: use readJson instead of imports for json

[connorjclark]

To prepare for using mocha instead of jest, we need to drop all the json imports (which jest supports, but mocha does not, because mocha is "just node").

I used a regex to do the bulk of the migration:

import (.*) from ('.*\.json')
const $1 = readJson($2, import.meta)

I also configured the max-len lint rule to ignore any line that uses readJson: ignorePattern: 'readJson\\(',

[brendankenny]

Can the incremental steps also wait on #14018? These lines were just all changed the other way in #13295 and I feel like we're in danger of hysteresis until we're sure we're going to make the mocha plunge (and not have to change our minds again if we run into some other immovable barrier)