Fix Dropdown Option Removal Regression

[TillerBurr]

Fixes #2733.

The tests for the option removal only included non-searchable dropdowns.

The problem was that the guard clause would always be false for searchable dropdowns and the props on the component were never updated, even though the React component was showing the expected behavior. Removing the !searchable reintroduced another issue (#2099), so there needed to be a way to know if there was a current search happening or if the options had actually been changed.

Instead of using searchable, create a state that is changed when the input is changed, indicating a search is being done. If there is a current search, don't update the options (and hence, don't render changes), else update the options.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Set a state variable for the search_value.
  • Use the state to check if it's an actual option change or just a search.
  • Parameterize the dropdown tests to make searchable True and False.
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[TillerBurr]

I changed it so it only checks !search_value and no extra state needed. From my testing and the included test, everything works as expected. All dropdown tests are passing locally.

The test could probably be simplified (i.e. 1 or 2 callbacks), but I wanted to make a clear distinction between the removal of the item and then checking the value afterwards.

[T4rk1n]

Looks good 💃