Upgrade ESLint packages

[andygout]

This PR upgrades all ESLint-related packages to their current latest version.

This includes a major upgrade of eslint from v8 to v9 which includes the breaking change of switching from a .eslintrc.json file to a .eslint.config.js file (migration guide).

Also, there is now only a single ESLint config file that sits at the root level rather than additional individual ESLint config files that sit within directories (e.g. test/.eslintrc.json), which have accordingly been removed in this PR.

It seems v9 of ESLint is clever enough to know when comments to disable certain rules are redundant and so this PR also removes those comments that have been flagged in:

• src/app.js
• src/contexts/CurrentPath.jsx

References:

• ESLint: Configuration Migration Guide
• ESLint: Introducing the ESLint Configuration Migrator
• GitHub: jsx-eslint/eslint-plugin-react — Issues: ESLint v9 contains breaking API changes
  • The changes in this PR were blocked until the issue described in this link were fixed by [New] support eslint v9 jsx-eslint/eslint-plugin-react#3759

New dev dependencies:

• globals
  • This is a dependency of eslint. Without globals v15 results in the following: eslint v9 TypeError: Key "languageOptions": Key "globals": Global "AudioWorkletGlobalScope " has leading or trailing whitespace. multiple globals. Installing globals as a direct dependency of this repo is required to ensure that v15 is used.