Break down ligatures in preprocessing to make search result more intuitive

[hehelego]

Is your feature request related to a problem? Please describe.

Many PDF file contains ligature substitution, so "fi" or "ff" becomes a single single character instead of two consecutive yet separate ones.
When you use ripgrep-all to search for string containing "fi" or "ff", the subsituted ones will not be matched.

Describe the solution you'd like
Break down common ligatures in rga-preproc.

Describe alternatives you've considered
Identify contractable ligatures in the search pattern and replace thme with (contracted)|(original).
For example, rga definition should actually search for de((fi)|X)nition where X is the ligature "fi".

Additional context

Backgrounds: wikipedia: ligatures in computer typesetting

The results are 27429, 5986, and 21451.