Issue #2275 - Entity Centre: floating and D'n'D for Insertion Points

[oleh-maikovych]

Resolve #2275

To be completed by the pull request creator

This section should be completed with reference to section Preparing PR of the Code and PR reviews wiki page.

• [x] Converted PR to draft while it is being prepared by tapping the "Convert to draft" link beneath the "Reviewers" section.

• [x] A self-review of all changes has been completed, and the changes are in sync with the issue requirements.

• [x] Changes to the requirements have been reflected in the issue description.

• [x] Any "leftovers" such as sysouts, printing of stack traces, and any other "temporary" code, have been removed.

• [x] Minor refactorings, such as renamings, extraction of constants, etc., have been addressed.

• [x] Developer documentation (e.g., comments, Javadoc), have been provided where required.

• [x] All existing and new Java tests pass successfully by running them with Maven.

• [ ] All existing and new Web tests pass successfully.

• [x] The correct base branch has been selected for these changes to be merged into.

• [ ] The latest changes from the base branch have already been merged into this feature branch (and tested).

• [ ] Added a change overview to the issue description or as a wiki page, referenced in the issue description. Some issue might be very descriptive and server in place of a wiki page. In such cases consider adding label Wiki like to the issue.

• [ ] This pull request does contain significant changes, the section "Significant changes" below is completed and at least one Senior Software Engineer with the relevant area of expertise has been selected as reviewer.

• [x] The In progress label has been removed from the issue.

• [ ] The Pull request label has been added to the issue.

• [ ] Made PR ready for review by tapping the "Ready for review" button below the list of commits on the PR page.

Additional details

Significant changes

To be completed by the pull request reviewer

This section should be completed with reference to section Performing PR review of the Code and PR reviews wiki page.

• [ ] The In progress label has been added to the pull request in GitHub.

• [ ] The issue requirements have been read and understood (along with any relevant emails and/or Slack messages).

• [ ] The correct base branch is specified, and that base branch is up-to-date in the local source.

• [ ] The issue branch has been checked out locally, and had the base branch merged into it.

• [ ] All automated tests pass successfully.

• [ ] Ensure the implementation satisfies the functional requirements.

• [ ] Ensure that code changes are secure and align with the established coding practices, including code formatting and naming conventions.

• [ ] Ensure that code changes are documented and covered with automated tests as applicable.

• [ ] Ensure that code changes are well-suited for informal reasoning.

• [ ] Ensure that changes are documented for the end-user (a software engineer in the case of TG, or an application user in the case of TG-based applications).

• [ ] If there are significant changes (described above), special attention has been paid to them. Marked the task items in section "Significant changes" as completed to indicated that corresponding changes have been reviewed, improved if necessary, and approved.

• [ ] The issue or issues addressed by the pull request are associated with the relevant release milestone.

To be completed by the pull request reviewer once the changes have been reviewed and accepted

• [ ] The changes have been merged into the base branch (unless there is a specific request not to do so, e.g., they are to be released to SIT).

• [ ] The issue branch has been deleted (unless the changes have not been merged - see above, or there is a specific request not to do so).

• [ ] The In progress label has been removed from the pull request.

• [ ] The Pull request label has been removed from the pull request.