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 <[email protected]>

python/sepolgen/src/sepolgen/refparser.py

@@ -261,7 +261,7 @@ def t_IDENTIFIER(t):
     return t
 
 def t_FILENAME(t):
-    r'\"[a-zA-Z0-9_\-\+\.\$\*~ :\[\]]+\"'
+    r'\"`*[a-zA-Z0-9_\-\+\.\$\*~ :\[\]]+\'*\"'
     # Handle any keywords
     t.type = reserved.get(t.value,'FILENAME')
     return t