Implement and use MultiArrayBuffer (#44980)

Implement and use MultiArrayBuffer (#44980)

* add MultiArrayBuffer and use in StreamBuffer and Http2Stream

* rework EnsureAvailableSpace and add tests for it

* make dispose handling more robust, plus minor tweaks

* add AssertExtensions.SequenceEqual for providing more useful information about sequence differences, and use in StreamConformanceTests

* tweaks

* replace _blockCount with _allocatedEnd

* use uint instead of int internally to assure bitop optimizations

* fix _allocatedEnd calculation

* address PR feedback

* more PR feedback and some minor fixes/improvements

* small test improvements

* Apply suggestions from code review

Co-authored-by: Günther Foidl <gue@korporal.at>
* address review feedback

Co-authored-by: Geoffrey Kizer <geoffrek@windows.microsoft.com>
Co-authored-by: Günther Foidl <gue@korporal.at>