Modernized blueprints. Dropped Node v18 support.

Since ember-codemod-v1-to-v2@1.0.0 (i.e. 2023, when the migration guide had been written), the blueprints from ember-cli and @embroider/addon-blueprint have changed, and several dependencies for an Ember project (e.g. eslint, ember-try) have introduced breaking changes through major releases.

As a result, if I simply let the codemod move files (i.e. use existing configurations and old versions of dependencies), the resulting project will become hard to fix for maintainers who are new to v2 addons. It's now a good time for the codemod to reset the project in a few ways:

• Configure linters (ember-template-lint, eslint, stylelint, and typescript).
• Configure .gitignore files.
• Install ember-try@v4.

ember-codemod-v1-to-v2@2.0.0 also introduces a couple of new features:

• Add addon.publicAssets() to rollup.config.mjs.
• Set up @embroider/broccoli-side-watch in test-app.

It follows @embroider/addon-blueprint@4.1.1 closely.