Fix AutoCorrection crashing with Missing extension point

[cortinico]

Fixes #4003
Fixes #4500
Fixes #4489

This issue was apparently caused by my PR #3848

What is happening is that KtLint is enabling AST mutation on the Root Extension, while we're not. Therefore, as the autoCorrect tries to mutate the AST it crashes with the mentioned message.

Moreover there was a ! missing which was causing the code to do nothing. I've also removed the syncronized as KtLint is not using it either.

I've tested locally with a SNAPSHOT version and it works for me. I'm unsure how we can test this with an automated test.

Sadly we will have to live with the deprecated getRootArea(). KtLint is having that as well so I guess they'll find a way if JetBrains decides to remove this API (and we'll have to follow their approach).

[codecov]

Codecov Report

Merging #4545 (d63d62c) into main (10e9e4c) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #4545      +/-   ##
============================================
+ Coverage     84.13%   84.14%   +0.01%     
- Complexity     3313     3315       +2     
============================================
  Files           477      477              
  Lines         10922    10920       -2     
  Branches       2030     2031       +1     
============================================
  Hits           9189     9189              
+ Misses          700      699       -1     
+ Partials       1033     1032       -1     

Impacted Files	Coverage Δ
...n/kotlin/io/github/detekt/parser/DetektPomModel.kt	72.22% <100.00%> (+7.22%)	⬆️

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