logarithmically smaller diff patches when changing expression trees

[jurgenvinju]

1. changes to expressions are very common when rewriting source code
2. expressions have a regular recursive structure, almost like lists
3. detecting common sub-expressions between the source and the target tree can be used to infer much smaller TextEdit instances than replacing the entire expression just because it has a different operator at the top.
4. the default treeDiff rule now replaces the entire expression, while the new code will replace/remove/add only an operator (for example), or only one side of the binary expression. This is logarithmically less damage to the input source code.

Cases currently tackled:

• removing prefix operator
• removing postfix operator
• removing left operand of binary operator
• removing right operand of binary operator
• removing brackets
• adding brackets

This PR will be finished when:

• a predictable number of cases have been tackled (coverage of typical expression tree modifications)
• all cases have at least one unit test case

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47%. Comparing base (c696a92) to head (45fde50).
⚠️ Report is 60 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##              main   #2484   +/-   ##
=======================================
- Coverage       47%     47%   -1%     
+ Complexity    6622    6618    -4     
=======================================
  Files          783     783           
  Lines        64703   64703           
  Branches      9688    9688           
=======================================
- Hits         30725   30715   -10     
- Misses       31578   31590   +12     
+ Partials      2400    2398    -2     

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