Devex/jsdoc migration

[brendanbond]

Link to Jira Ticket

n/a

Description

Upgrades our ESLint configuration and introduces a jsdoc plugin to encourage developers to use JSDoc syntax to loosely type functions, objects, and values throughout the formio.js library. (In the build process, Typescript will use these annotations to generate type definitions - they're not perfect, but they're far better than nothing.)

Dependencies

n/a

How has this PR been tested?

n/a

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above