Search option in card template editor

**Is your feature request related to a problem? Please describe.**
The search option will be helpful in card template editor to quickly find the known strings.

**Describe the solution you'd like**
Search option in options menu

**Describe alternatives you've considered**
The alternative will be copy the card templates content to different editor and edit there.

**Additional context**
AnkiDesktop has the seach box in card template editor.