Encapsulate global constants in namespace of surrounding type

[mx990]

This is necessary to avoid name collisions or ambiguity between constants declared in the same package but in distinct files, as well as with variables declared in the current scope. It also puts an end to the special treatment of global constants being available directly outside of the scope of their enclosing type.

Add a new GLOBALCONSTANTS syntax element to represent the enclosing type:

PACKAGE forte::core;

GLOBALCONSTANTS Math
    VAR_GLOBAL CONSTANT
        PI : REAL := 3.14159;
    END_VAR
END_GLOBALCONSTANTS

and refer to constants using either:

• the full-qualified name forte::core::Math::PI,
• the semi-qualified name Math::PI with an import for forte::core::Math (preferred),
• the unqualified name PI with an import for forte::core::Math::PI or forte::core::Math::* (discouraged).

[azoitl]

@franz-hoepfinger-4diac & @moniwe just to pre-warn you, this change will require that you need to update your global constants.