Fix vue/component-definition-name-casing violations

This issue tracks the fixing of violations of the vue/component-definition-name-casing rule (see #296868 (closed)) and the removal of the rule override.

This may be fixable via ESLint.

Implementation plan

• Remove the rule override, run yarn run eslint-fix, and create MRs for each top-level directory (rather than one big MR, to minimise merge conflicts - unless the set of changes isn't huge, in which case one MR will do)