Add ecompile flag -Z to print AST (#796)

* Add -Z option to print string tree

* Simple test to print an AST

* Make CompiledScript owner of the tree

* some refactoring
- rename ecompile.cfg option
- rename AST generator class

* core-changes, docs

* fix warnings

pol-core/bscript/compiler/codegen/AbstractSyntaxTreeStringGenerator.cpp

@@ -0,0 +1,15 @@
+#include "AbstractSyntaxTreeStringGenerator.h"
+
+#include "bscript/compiler/ast/Node.h"
+#include "bscript/compiler/file/SourceFileIdentifier.h"
+
+namespace Pol::Bscript::Compiler
+{
+AbstractSyntaxTreeStringGenerator::AbstractSyntaxTreeStringGenerator() {}
+
+void AbstractSyntaxTreeStringGenerator::visit_children( Node& parent )
+{
+  if ( parent.source_location.source_file_identifier->index == 0 )
+    _tree += parent.to_string_tree();
+}
+}  // namespace Pol::Bscript::Compiler