fix(admin-panel): trim whitespace from admin panel search bar

[millmason]

Because:

• When copying and pasting values into the search bar, it's easy to accidentally include whitespace either before or after the copied value. Currently, this will result in the search not returning a result (as it will search for the entire input, including whitespace.)

This pull request:

• Trims the search input value before we submit it to the search (in the handleSubmit action, in the input length check that determines whether or not to show suggestions, and also in the search that returns suggested matching emails.) There is a slightly simpler way to this -- we could just trim
  "event.target.value" before it's set into state using setSearchInput, but this could result in the user trying to type
  in the input (with spaces, for example) and thinking they couldn't interact with the search input (since the value of the search input would be constantly trimmed). While slightly more complicated, I think this is a safer solution.

• There also seemed to be a duplicate setSearchInput action happening in onTextChanged, which I have removed. onTextChanged seems to only ever be called by handleChange, which already calls setSearchInput.

Closes #12567

Checklist

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• My commit is GPG signed.
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• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

Screenshots

Before (whitespace before or after search input value is included in query term and returns nothing):

After (whitespace is trimmed and search returns correct record):

[dschom]

LGTM! Thanks for the fix! I have one very small nitpick, that you should feel free to ignore if you like. It seems like this could have been done in fewer lines on the server side or whenever the value is set (as opposed to when it's read). Either of these approaches might be seen as a bit more DRY and indicate a more maintainable solution.

[millmason]

@dschom That's a really interesting idea, I'll look into it!

[millmason]

@dschom I looked into this and we can transfer trimming the strings out of the frontend, but it will be handed off to GraphQL, so I think it would be harder to maintain (since there are a few different GraphQL methods, so the duplication would be obscured.) My issue with trimming the string where it was set is that I think it's a confusing interaction for the user -- if the user enters whitespace into the search input, it will look as if the search input is broken (because the whitespace characters don't show up.) That being said, the only reason why the whitespace was introduced was due to copy-pasting values -- not due to a user typing whitespace into the search input. Also maybe we should prioritize code readability over covering all corners of the user experience since this is purely admin-facing. What do you think?

[dschom]

@millsoper I think it's good to go then! I had my suspicions that doing it in the set resulted in a glitchy ux in some cases. This was truly just a nitpick, and I was mostly was curious if/why this approach was used over the others.