[Debug] Escape LLDB syntax in debugDescription (#75300)
- **Explanation**:
When using `@DebugDescription`, only allow use of [LLDB Summary
Strings](https://lldb.llvm.org/use/variable.html#summary-strings) syntax from
`lldbDescription` properties. When `@DebugDescription` is applied to existing
`debugDescription` properties, escape any `$`, as the output of `debugDescription` is
never interpreted by LLDB.
- **Scope**:
This will not break existing code. Adopters will almost certainly be unaffected.
- **Original PRs**:
https://github.com/swiftlang/swift/pull/75300
- **Risk**:
No risk, it fixes a potentially surprising bug if an existing `debugDescription` was
reused with this macro, and the string contained the substring `${`.
- **Testing**:
Swift tests, CI.
- **Reviewers**:
@hborla, @stephentyrone, @DougGregor
