Removing unnecessary allocations and more

[JustForFun88]

This pull request does:

• removes a lot of unnecessary memory allocations. For example, previously, multiple allocations of vectors were performed in a loop to store a single character (function lapce_core::syntax::Syntax::find_matching_pair);
• removes many indirect function calls. For example calling ~~to_string() on a &' static str~~, using "".to_string() instead of String::new().

In addition, a complete rewrite of the Snippet::extract_text function was performed while preserving the logic of its work. This was done, firstly, to remove the constant copying of immutable vectors in a loop. Secondly, to exclude a possible crash of the program, since accessing an element by index for a string is not a good idea.

• [ ] Added an entry to CHANGELOG.md if this change could be valuable to users

[panekj]

~~what's wrong with String::new()?~~ misread that

[codecov-commenter]

Codecov Report

Merging #1796 (0551acb) into master (7a2f342) will increase coverage by 0.76%. The diff coverage is 72.02%.

@@            Coverage Diff            @@
##           master   #1796      +/-   ##
=========================================
+ Coverage    6.39%   7.16%   +0.76%     
=========================================
  Files         128     129       +1     
  Lines       55350   55861     +511     
=========================================
+ Hits         3542    4000     +458     
- Misses      51808   51861      +53     

Impacted Files	Coverage Δ
lapce-core/src/cursor.rs	5.11% <0.00%> (-0.02%)	:arrow_down:
lapce-core/src/lib.rs	100.00% <ø> (ø)
lapce-core/src/syntax/mod.rs	7.30% <0.00%> (+0.02%)	:arrow_up:
lapce-data/src/alert.rs	0.00% <0.00%> (ø)
lapce-data/src/config.rs	0.00% <0.00%> (ø)
lapce-data/src/data.rs	0.00% <0.00%> (ø)
lapce-data/src/db.rs	0.00% <0.00%> (ø)
lapce-data/src/document.rs	0.00% <0.00%> (ø)
lapce-data/src/editor.rs	0.00% <0.00%> (ø)
lapce-data/src/keypress/mod.rs	16.38% <0.00%> (ø)
... and 38 more

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[JustForFun88]

@panekj Made requested fixes and improved some of my solutions. I think this pull request is ready for another review.

[panekj]

Where is the CharBuffer from (and why)?

[JustForFun88]

Where is the CharBuffer from (and why)?

I wrote it myself as a helper structure to store a one-character &str on the stack instead of on the heap. I thought it would be a useful structure both now and later.

And well, since this is a structure for storing a "string slice", then it must be done correctly so that it can be compared with other string structures, converted from one structure to another and vice versa, it must have documentation and tests.

The name may not be very good, but I couldn't think of a better one.

[panekj]

Is there anything left to do?

[JustForFun88]

Is there anything left to do?

Yes, I need to clean up the PR by removing things that have already merged. Can't do it right now as I'm busy developing generic traits for containers/collections.