com.unity.collections 2.1.0-exp.4 Package Notes

`Native/Unsafe/FixedList.InsertRange` with index/count arguments.
StreamCompressionModel moved from com.unity.transport
DataStreamReader moved from com.unity.transport
DataStreamWriter moved from com.unity.transport
Job types depending on collections have been moved here
Burst compiled delegates for allocators are now cached, which avoids a costly re-compilation
`DataStreamReader` can now be passed to a job
`DataStreamReader` can now be passed to a job.
IJobParallelForBatch from com.unity.jobs
`Unsafe/NativeHashMap/Set` suitable for single-threaded use cases.
`Native/UnsafeHashSet.ReadOnly` and `Native/UnsafeParallelHashSet.ReadOnly`.
`ConvertExistingDataToNativeArray` in `CollectionHelper` for custom allocators.
`Native/UnsafeBitArray.ReadOnly`.
CopyFromTruncated for one FixedStringXXXBytes to another FixedStringYYYBytes
New method `AddReplicate` to `NativeList`, `UnsafeList` and all `FixedList`, which will add a value `count` times to the list.
`CollectionHelper.CreateSafetyHandle` and `CollectionHelper.DisposeSafetyHandle` are public APIs now.

T constraint on all containers from `struct` to `unmanaged`
Add the missing string interpolation operator in two memory exception messages and make the message clearer.
Awareness of newly supported nested containers
Faster FixedString comparison
Reset `m_best` in RewindableAllocator rewind.
IJobParallelForFilter renamed to IJobFilter to better reflect functionality
Ensure lazy initialization of IJob types
Change Bool type, `m_enableBlockFree` in `RewindableAllocator` to Byte type.
Change the growth rate of memory block size in RewindableAllocator.
FixedList methods `AddRange` and `AddRangeNoResize` will no longer append elements if they would exceed capacity.

Some `AssumePositive` assumptions that should have been after some safety checks but weren't.
`Native/UnsafeList.InsertRangeWithBeginEnd` to allow end argument to resize list.
Fixed a race condition in the parallel hashmap when using `ParallelWriter` with hashmaps that operate close to their capacity
Update documentation on existing DataStream structs and helper methods.
Don't cache `DataStreamWriter.IsLittleEndian`, as the cache could not be properly populated if its shared static was not 0-initialized.

DisposeSentinel usage in containers.
deprecated code untyped `UnsafeList`, and `WordStorage`.
All deprecated code.
Temporary NativeArray placeholder
### Deprecated
NetworkCompressionModel. New type StreamCompressionModel is no longer IDisposable and all usage of this should use the SharedStatic reference instead.
Packed read and write methods that take NetworkCompressionModel as a parameter. New versions taking StreamCompressionModel as an argument should be used instead.
`UnsafeList.ParallelReader` replaced by `UnsafeList.ReadOnly`.
`NativeList.AsParallelReader()` replaced by `NativeList.AsReadOnly()`.
Implicit cast operator from `NativeList` to `NativeArray`. Explicit cast method `NativeList.AsArray()` should be used instead.

com.unity.collections 2.1.0-exp.4