feat: Add local search in buffer

[oxcrow]

Hi everyone,

I added a feature to do local search in the currently opened document buffer to improve user experience.

This feature is similar to global_search but is only limited to one document.

The command is activated by space+l and seems to work well.

Kindly review and allow this feature to be merged.

Thank you
~oxcrow

Reasoning

• The global_search method is quite nice since it works in a fuzzy finding method and provides a table of matches that we can easily preview to find what we want.
• A similar feature is needed for searching through the currently opened buffer (i.e only one document). We could use global_search however it produces too many false positive results from other files, which makes it difficult to use.
• The standard local search method using / does not feel very good to use.
• Other editors such as Emacs/Neovim provide plugins for local search such as Swiper, which feel better to use https://github.com/abo-abo/swiper
• This feature is implemented to provide a similar feature as Swiper.

Implementation

• I took the code of global_search and modified it little bit.
• Specifically I modified the code to only search through the current document.
• The code works but it should be improved by someone more experienced (if necessary).

[nik-rev]

Showing the path to the file in the global search picker where there can be lots of files makes sense. But here it doesn't really make sense, because you're searching in the same file - so all picker items will show the same path

Maybe instead of showing the path, show the line number and the string contents of that line in the 2nd column