Handle copy replacing with ==::==

[smedilol]

Describe the bug
Our parser cannot use standard Cobol Copy with a replacing clause containing string ::.

       01  xxxENT. COPY YxxxENT REPLACING ==::== BY ====. 

YxxxENT contains:

           05  xxxENT::-FCT01.
               10 xxxENT::-FCT01-Var1            PIC X(05).

The parser interpret :: as TypeCobol operator but inside a replacing clause (Pseudo text), this operator should be considered as plain text.

Expected behavior
No error.
The expanded source is:

       01  xxxENT. 
           05  xxxENT-FCT01.
               10 xxxENT-FCT01-Var1            PIC X(05).

Technical
See Scanner class and use property IsInsidePseudoText of the ScanState to inhibit creation of token :: inside pseudo text.

[fm-117]

Testing for IsInsidePseudoText won't be enough, we'll have to allow the creation of a PartialCobolWord for text :: and double colon must be replaced correctly while parsing the copy (as for now :: will be materialized as a QualifiedNameSeparator token).
It means that interpretation of the text :: inside a copy depends on the active REPLACING clause.
See #428 for other out-of-ordinary REPLACING clauses.
One way to tackle this could be to avoid creating original tokens of a copy but only create the replaced ones. This is a rather large change of the Scanner though...

[rooksdo]

To be in conformity with the specifications, replacing clause should handle any placeholder between ==[placeholder]==.

Also, scanning should have two modes :

1. Program mode
2. Copy mode
   • For the copy mode, we should be able to distinguish between EI_Release and regular Release environment.
     => EI_Release copys will not allow Cobol statements (Move, Perform...)
   • In all cases, TypeCobol inside copys is not handled, so :: should never be interpreted as TypeCobol operator inside a copy or in a replacing statement.

[smedilol]

@fm-117 @mayanje Goal for this issue: In the scanner:
Inside a copy, do not recognize the :: operator. Only recognize two : in a row.