[5.1] Rewrite com_associations in vanilla JS

[C-Lodder]

Summary of Changes

This PR addresses two items:

1. Two of the toolbar buttons ("Save Target" and "Copy Reference to Target") were missing an ID and therefore were not hidden as the JS couldn't find them.
2. Remove the jQuery dependency for the com_associations sidebyside JS

Testing Instructions

1. Ensure you have a multilingual site setup.
2. Play around with com_associations and make sure it's all working as expected.

[ghost]

@C-Lodder please inform when the PR is ready for test.

[C-Lodder]

@fgsw It's ready now

[ghost]

I have tested this item ✅ successfully on be13537

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[Fedik]

@C-Lodder I see you are brave man.
The whole thing is asking for a good refactoring, but moving away from jquery, at least something.
Thanks!

And please keep old copyright date, in the end it the same sidebyside.js

[LadySolveig]

Thank you @C-Lodder and also for testing and review @fgsw @Fedik @laoneo @dgrammatiko