Don't use PSI for line number calculation

[petertrr]

What's done:

• Changed logic
• Added test

Which rule and warnings did you add?

We were trying to use cached value of line number from PSI ViewProvider, but if the tree is changed in fixMode, ViewProvider is not updated. This causes it to return invalid offsets.

This pull request closes #934

[codecov]

Codecov Report

Merging #950 (d7f9788) into master (93bfd08) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #950      +/-   ##
============================================
+ Coverage     84.11%   84.13%   +0.02%     
- Complexity     2392     2394       +2     
============================================
  Files           101      101              
  Lines          6030     6025       -5     
  Branches       1783     1780       -3     
============================================
- Hits           5072     5069       -3     
  Misses          263      263              
+ Partials        695      693       -2     

Flag	Coverage Δ
unittests	84.13% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
...t/rules/chapter3/identifiers/LocalVariablesRule.kt	91.08% <ø> (ø)
...tlin/org/cqfn/diktat/ruleset/utils/AstNodeUtils.kt	85.54% <100.00%> (+0.10%)	⬆️
.../ruleset/rules/chapter3/files/FileStructureRule.kt	83.03% <0.00%> (+0.60%)	⬆️

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