sepolgen-ifgen: allow M4 escaped filenames

When a file name in type transition rule used in an interface is same as
a keyword, it needs to be M4 escaped so that the keyword is not expanded
by M4, e.g.

-	filetrans_pattern($1, virt_var_run_t, virtinterfaced_var_run_t, dir, "interface")
+	filetrans_pattern($1, virt_var_run_t, virtinterfaced_var_run_t, dir, ``"interface"'')

But sepolgen-ifgen could not parse such string:

    # sepolgen-ifgen
    Illegal character '`'

This change allows M4 escaping inside quoted strings and fixed described
problem.

https://bugzilla.redhat.com/show_bug.cgi?id=2254206

Signed-off-by: Petr Lautrbach <lautrbach@redhat.com>

python/sepolgen/src/sepolgen/refparser.py

@@ -486,7 +486,7 @@ def p_interface_call_param(p):
                             | nested_id_set
                             | TRUE
                             | FALSE
-                            | FILENAME
+                            | quoted_filename
     '''
     # Intentionally let single identifiers pass through
     # List means set, non-list identifier
@@ -1027,6 +1027,11 @@ def p_optional_semi(p):
                    | empty'''
     pass
 
+def p_quoted_filename(p):
+    '''quoted_filename : TICK quoted_filename SQUOTE
+                       | FILENAME
+    '''
+    p[0] = p[1]
 
 #
 # Interface to the parser