"readonly" error (XBase++)

[DenGhostYY]

Describe the bug
The compiler throws an error due to assignment of a "readonly" field in the context of a method of the same class.

To Reproduce

procedure main()
    local o := Example():new(4)

    ? o:nNumber
//    o:nNumber := 10
    o:SetNumber(15)
    ? o:nNumber
return


class Example
exported:
    var nNumber readonly

    inline method init(nNumber)
        ::nNumber := nNumber
    return

    inline method SetNumber(nNumber)
        ::nNumber := nNumber
    return self
endclass

Expected behavior (XBase++ exe)
Output

4
15

Actual behavior (X# compiler)

error XS0191: A readonly field cannot be assigned to (except in a constructor or init-only setter of the type in which the field is defined or a variable initializer)

Additional context
X# Compiler version 2.20.0.3 (public)
-dialect:xBase++
-codepage:866
-lb -enforceself -memvar -xpp1 -vo1 -vo3 -vo4 -vo5 -vo9 -vo10 -vo12 -vo13 -vo14 -vo15 -vo16 -vo17
-reference:XSharp.Core.dll
-reference:XSharp.RT.dll
-reference:XSharp.XPP.dll

[nvkokkalis]

Fix is similar to #1491; same problems apply.