Generic class constructor with generic-typed default parameter (`= nil`) fails to parse

[mksjgj]

Summary
DelphiAST cannot parse a syntactically valid unit where a generic class
constructor has a parameter whose type depends on the generic parameter and a
default value, e.g. constructor Create(AFinProc: TProc<T> = nil);.
Removing = nil makes the identical unit parse fine.

Minimal reproducer (Repr.pas)

unit Repr;
interface
uses
  SysUtils;
type
  C<T> = class
    constructor Create(AFinProc: TProc<T> = nil);
  end;
implementation
end.

How to reproduce with DelphiAST
program t;
{$APPTYPE CONSOLE}
uses
  DelphiAST, DelphiAST.Classes;
var
  AST: TSyntaxNode;
begin
  try
    AST := TPasSyntaxTreeBuilder.Run('Repr.pas', False);
    Writeln('parsed OK');
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);   // parse error
  end;
end.

Control (Ctrl.pas, parses fine — only = nil removed)
unit Ctrl;
interface
uses
  SysUtils;
type
  C<T> = class
    constructor Create(AFinProc: TProc<T>);
  end;
implementation
end.

Narrowing (all tested individually, only the failing combo fails)
- AFinProc: TProc<T> = nil (default on generic-typed param) → fails
- AFinProc: TProc<T> (no default) → parses
- FinType: Integer = 0 (default on non-generic param) → parses
- plain generic class / generic method / record with generic field / class helper /
  untyped const/out param / BOM / {$IFDEF} / {$IF CompilerVersion<36} /
  (* *) comments → all parse fine

Why it matters
I discovered this through a tool (delphi-indexer) that embeds DelphiAST: real
units using this pattern parse to 0 nodes and are silently dropped from the
index (e.g. TResHolder<T> = class(TInterfacedObject, IResHolder<T>) with
constructor Create(..., AFinProc: TProc<T> = nil);), leaving whole libraries
unsearchable. I assume the fault is in how the parser handles a default value
on a parameter whose type references the enclosing generic type.

Environment: Delphi 12.3 · DelphiAST current (bundled version in delphi-indexer).
Happy to help test a fix or provide the exact DelphiAST version/commit.