rework stripMultilineComments to handle one comment being removed changing the offsets of the others

Author: Numpsy

src/FSharpLint.Core/Rules/Conventions/SourceLength/SourceLengthHelper.fs

@@ -46,13 +46,21 @@ let internal stripMultilineComments (source: string) =
         |> Seq.sortBy (function | Begin index -> index | End index -> index)
         |> Seq.toList
 
-    getTopLevelBalancedPairs markers List.Empty
-    |> List.fold
-        (fun (currSource: string) (startIndex, endIndex) ->
-            let left = currSource.AsSpan(0, startIndex) 
-            let right = currSource.AsSpan(endIndex + multilineCommentMarkerRegexCaptureGroupLength)
-            String.Concat(left, right))
-        source
+    match getTopLevelBalancedPairs markers List.Empty with
+    | [] -> source
+    | pairs ->
+
+        let builder = Text.StringBuilder(source)
+
+        // Remove each comment block in turn
+        // Keep track of the count of characters removed in order to patch the offsets when removing test changes them
+        pairs
+        |> List.fold
+            (fun (currSource: Text.StringBuilder, removedCharsCount) (startIndex, endIndex) ->
+                let length = endIndex - startIndex + multilineCommentMarkerRegexCaptureGroupLength
+                (currSource.Remove(startIndex - removedCharsCount, length), removedCharsCount + length))
+            (builder, 0)
+        |> (fst >> _.ToString())
 
 let checkSourceLengthRule (config:Config) range fileContents errorName (skipRanges: array<Range>) =
     let error name lineCount actual =