Add find functionality

What does this MR do and why?

This MR adds the Find functionality to the Find And Replace logic. It's part of a series of MRs. With this MR the following functionalities are introduced:

• Highlight text that is being search
• Close the Find And Replace bar on Escape key press
• Remove artifacts generated when the find and replace bar is closed and restore to the normal state

References

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Screenshots or screen recordings

find

How to set up and validate locally

1. Enable feature flag: find_and_replace
2. Visit an issue or a merge request
3. Edit the description
4. When edit mode is turned on, hit CMD+F
5. Type in something in the box that opens
6. It should highlighted the searched text

Related to #481892 (closed)