Shortcut to search and auto highlight search bar

[AzulRadio]

Signed-off-by: youhy haoyuan2019@outlook.com

New feature(s)

Summary

There are 2 features added in this PR. Both of them are small and are about the search bar/menu so I combine them into one PR.

Feature 1. When we close the search bar for adding plugins, the text in it will be preserved. If we want to add another plugin, we need to delete the first one. That's a little annoying. Now after adding a plugin, text in the search bar will be auto highlighted so the search bar can be cleared easier.

No highlight if no plugin is added.

Feature 2. Press / to open the plugin search bar

Test it

Try it

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #405 (2ae2ee5) into ign-gui6 (5d5755c) will not change coverage.
The diff coverage is n/a.

❗ Current head 2ae2ee5 differs from pull request most recent head df93a84. Consider uploading reports for the commit df93a84 to get more accurate results

@@            Coverage Diff            @@
##           ign-gui6     #405   +/-   ##
=========================================
  Coverage     30.54%   30.54%           
=========================================
  Files            41       41           
  Lines          1748     1748           
=========================================
  Hits            534      534           
  Misses         1214     1214           

Impacted Files	Coverage Δ
include/ignition/gui/qrc_resources.cpp	100.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5d5755c...df93a84. Read the comment docs.