<c-f> now focuses on search entry if already shown

Previously, <c-f> would only show the search bar if the search bar had not already been revealed within the tab. This pertains to #153 (closed) .

Now, will show the search bar and if already shown then focusses the search entry within the search bar.

I am interested in participating in GSOC 2022, and am going to apply for Gtranslator project idea. This is my first contribution to an open source project. I have been trying to familiarize myself with the code base through the last couple of days.

Your feedback would be really helpful. Thank you.

Edit: *typo, added issue link