Add Nettrace compression and multi-process support

[mjsabby]

• Adds C# implementation for LZ-based compression and decompression that is used in BPerf File Format (the file format we're intending to replace)
• Adds a flag for the compression type
• Adds next 4 bytes to header, this is the decompressed size.

[mjsabby]

cc @noahfalk

[brianrob]

@mjsabby, are there corresponding runtime changes for this?

[mjsabby]

@brianrob The runtime does not yet emit this. @noahfalk wanted the file format to be settled on first. We will have our tool generate it, and then hopefully I can port it to the runtime as an option as well.

[mjsabby]

@noahfalk If you could do a once over to see if this is the direction you wanted ...

[noahfalk]

@noahfalk If you could do a once over to see if this is the direction you wanted ...

Direction seemed fine to me, thanks @mjsabby! I spotted a few things in the details I commented on above

[noahfalk]

cc @josalem @sywhang