This improves the handling of `$` (dollar) characters in summary strings in the
following ways:
1. When a `$` is not followed by an open paren (`{`), it should be treated as a literal
character and preserved in the output. Previously, the dollar would be consumed by the
parser and not shown in the output.
2. When a `$` is the last character of a format string, this change eliminates the
infinite loop lldb would enter into.
rdar://131392446
10f3f06d86