VersionAlert for Unity

When Burst is disabled via the `UNITY_BURST_DISABLE_COMPILATION` environment variable, Burst's IL postprocessor is also now disabled
Invoking `GetUnsafePtr()` on any `NativeContainer` collection type inside a job struct will now return a pointer that is assumed to `[NoAlias]` with other `NativeContainer` collection types within the same job struct (previously this was just the case with `NativeLists` and `NativeArrays`)
Set the default LLVM version in use to LLVM 19
Changed Burst minimum editor version to 2021.3

Added support for cross-compiling Burst code for iOS, tvOS, and visionOS from Linux and Windows. Note that a Mac is still required to build the resulting Xcode project.

Fixed compiler crash when using a non-`int` value value loaded from a field for bitshifting a vector type
Fixed that Burst wouldn't use new versions of previously installed package assemblies if they were installed in that same session
Fixed the alias performance regression when using LLVM 19, that was introduced in Burst version 1.8.21 (when LLVM 19 support was added)
Fixed "no platform load command found" Xcode build warnings for Burst binaries that could occur in iOS / tvOS / visionOS player builds
The `burst.initialize.static.*` functions now only invoke the static constructors actually used by the associated entry point . Similarly, `burst.initialize.externals.*` only set up the externals invoked by the associated entry point.

com.unity.burst 1.8.22