Injection Fixes

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These changes aim to resolve issues with the new injection system.

Injections are now dynamically checked as part of the main interval.
We check for injections by query selecting the injected elements and checking if they are marked as being injected (via an attribute).
This way, if old shorts are loaded and the injected elements are removed, we can react to that and inject them again.

This unfortunately removes the error messaging, but Im not sure if that was particularly useful anyway

When adding new injected elements, you now should:

• Add a new enum for the element to InjectionItemsEnum (unless its a child of one thats already there)
• Add <your element>.setAttribute(INJECTION_MARKER, ""); to your method that inserts the new element
• Add a new case for your element in injectIfNotPresent() - you can just copypaste one thats there (note the getter should be for the element that has the marker)

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List of issues this may resolve:

• Seek feature not working #223
  likely caused by progress bar not being reinjected after removal

• Volume slider disappear after navigation to the next shorts #230
  volume not being reinjected after removal

• Timeline slider breaks after scrolling to the next short #236
  progress bar not being reinjected after removal

(there may be more)

[ynshung]

Thanks for the fix!