fix(detectors/goto): missing PosEx import + CharInSet for WideChar set

Two compiler issues hit on the user's Delphi 12 build:

  E2003 Undeklarierter Bezeichner: 'PosEx'  (line 81)
  W1050 WideChar in Set-Ausdruecken auf ByteChar verkuerzt  (line 147)

PosEx lives in System.StrUtils, which we use in uWithStatement /
uReversedForRange but I forgot to add to this new unit's uses clause.

The 'c in ['g','G']' check truncates the WideChar 'c' to ByteChar.
Standard Unicode-Delphi fix is CharInSet from System.SysUtils (already
imported). uReversedForRange and uWithStatement use the same pattern
elsewhere.

No behavior change otherwise - the detector logic is unchanged.

Author: nrodear

StaticCodeAnalyserForm/sources/Detectors/uGotoStatement.pas

@@ -42,6 +42,7 @@   TGotoStatementDetector = class
 implementation
 
 uses
+  System.StrUtils,                 // PosEx
   uFileTextCache;
 
 const
@@ -144,7 +145,9 @@ function FindGoto(const Line: string; var InBlockComm: Boolean;
       Continue;
     end;
     // `goto`-Match: case-insensitive, beidseitige Wortgrenze.
-    if (c in ['g','G']) and (i + KW_LEN - 1 <= n) and
+    // CharInSet statt c in [...] - WideChar (= Char in Unicode-Delphi) waere
+    // sonst implizit auf ByteChar verkuerzt (W1050).
+    if CharInSet(c, ['g','G']) and (i + KW_LEN - 1 <= n) and
        SameText(Copy(Line, i, KW_LEN), KW) then
     begin
       // Linke Wortgrenze: vorheriges Zeichen nicht-ident