Use @rollup/plugin-terser to minify JS

[IanDelMar]

Description

This PR

• uses @rollup/plugin-terser to minify JS instead of using terser directly.
• adds necessary changes to rollup.config.js.
• transforms terser.config.JSON to terser.config.js.
• removes Popper from the globals object as it is bundled for both Bootstrap 4 and 5.

Motivation and Context

It's no longer necessary to split the JS build task into one for compilation and another one for minification - both is handled via rollup now.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Development (changes that affect the build system or external dependencies)

Checklist:

• I pulled my branch from develop.
• I am submitting my pull request to develop.
• I have resolved any conflicts merging this pull request would create.
• I have checked that there aren't other open Pull Requests for the same update/change.
• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have read the CONTRIBUTING document.

Related Issues or Roadmap requests

Further comments