For #18729 - Use consistent string naming for generic strings

[gabrielluong]

Fixes #18729

We don't use R.string.edit anywhere except in a nav_graph label and snackbar test. https://github.com/mozilla-mobile/fenix/search?q=R.string.edit. So, I am moving that up to where we have our generic strings. I think this is sufficiently generic that we don't need to create a new edit_label string as done in #18555 (comment).

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

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[codecov-io]

Codecov Report

Merging #18730 (fd37440) into master (2687092) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master   #18730      +/-   ##
============================================
- Coverage     33.45%   33.44%   -0.02%     
- Complexity     1435     1436       +1     
============================================
  Files           499      499              
  Lines         20504    20540      +36     
  Branches       3094     3100       +6     
============================================
+ Hits           6860     6869       +9     
- Misses        12796    12824      +28     
+ Partials        848      847       -1     

Impacted Files	Coverage Δ	Complexity Δ
...lla/fenix/components/toolbar/DefaultToolbarMenu.kt	3.30% <0.00%> (ø)	2.00 <0.00> (ø)
...a/org/mozilla/gecko/search/SearchWidgetProvider.kt	24.00% <0.00%> (-6.77%)	1.00% <0.00%> (ø%)
...java/org/mozilla/fenix/perf/PerformanceInflater.kt	95.00% <0.00%> (+15.00%)	5.00% <0.00%> (+1.00%)

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[mergify]

This pull request has conflicts when rebasing. Could you fix it @gabrielluong? 🙏