[turbopack] Create a macro rcstr! for constructing RcStr from string literals. (#79759)
## Add `rcstr!` macro for efficient string literal handling
### What?
This PR introduces a new `rcstr!` macro that creates `RcStr` instances from string literals, optimizing for inline storage when possible and using `LazyLock` for longer strings.
### Why?
The `rcstr!` macro provides several benefits:
- Allows compile-time evaluation of inline strings
- Caches longer strings using `LazyLock` to avoid repeated allocations