A fix for handling nested parentheses in sass (#12833)

Selectors such as *:not(:lang(fr)) are now allowed. Nested
parentheses were identified as the cause of the problem. Now
skipping is done to the matching right parenthesis instead of the
first right parenthesis.

Change-Id: I2e83cac14796b739c6b6550642417b12dab752f2