Add a gold test case for $'', derived from a problem found in the lexer.

gold/dollar-sq.sh

@@ -0,0 +1,6 @@
#!/bin/bash

echo $'foo\tbar\n'

echo $'foo\tbar\n\
baz'

test/gold.sh

@@ -106,6 +106,8 @@ complex-here-docs() {

comments() { _compare gold/comments.sh; }
export() { _compare gold/export.sh; }
# Not implemented in osh.
dollar-sq() { _compare gold/dollar-sq.sh; }

# Needs declare -p
declare() { _compare gold/declare.sh demo; }