Extract SemanticVersion into its own crate (#9956)

This PR extracts the `SemanticVersion` out of `util` and into its own
`SemanticVersion` crate.

This allows for making use of `SemanticVersion` without needing to pull
in some of the heavier dependencies included in the `util` crate.

As part of this the public API for `SemanticVersion` has been tidied up
a bit.

Release Notes:

- N/A

crates/gpui/src/platform.rs

@@ -53,10 +53,10 @@ pub use keystroke::*;
 pub(crate) use linux::*;
 #[cfg(target_os = "macos")]
 pub(crate) use mac::*;
+pub use semantic_version::SemanticVersion;
 #[cfg(any(test, feature = "test-support"))]
 pub(crate) use test::*;
 use time::UtcOffset;
-pub use util::SemanticVersion;
 #[cfg(target_os = "windows")]
 pub(crate) use windows::*;