Add `LOCAL spvar` syntax for prepared statements and SYS_REFCURSORs

Under terms of this task we'll implement a number of extensions into prepared statements and SYS_REFCURSORS:

New functionality for prepared statement

PREPARE LOCAL

PREPARE LOCAL spvar_with_ps_name FROM 'dynamic sql';

Prepare a PS using an SP variable value as the PS name

EXECUTE LOCAL

EXECUTE LOCAL spvar_with_ps_name;

Execute a PS using an SP variable value as the PS name

DEALLOCATE PREPARE LOCAL

DEALLOCATE PREPARE LOCAL spvar_with_ps_name;

Deallocate a PS using an SP variable value as the PS name

New functionality for SYS_REFCURSORS

OPEN FOR LOCAL

OPEN c0 FOR LOCAL spvar_with_ps_name;

Open a SYS_REFCURSOR from an already prepared statement whose name is in an SP variable

OPEN FOR PREPARE

OPEN c0 FOR PREPARE stmt;

Open a SYS_REFCURSOR from an already prepared statement