Improvements on React and Angular integration pages

[tiny-ben-tran]

Ticket: DOC-

Site: Staging branch

Changes:

• Removed duplicated and scattered guide on including premium plugins in integration pages
• Corrected the instructions on several pages
• Added a guide for bundling tinymce from .zip package in Angular

Pre-checks:

• [ ] Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.
• [ ] modules/ROOT/nav.adoc has been updated (if applicable).
• [ ] Included a release note entry for any New product features.
• [ ] If this is a minor release, updated productminorversion in antora.yml and added new supported versions entry in modules/ROOT/partials/misc/supported-versions.adoc.

Review:

• [ ] Documentation Team Lead has reviewed