[release/6.0] Use ArrayPool as default pool fallback (#36253)

* Use ArrayPool as SlabMemoryPool fallback

Fixes #30364

* Fix comments

* Typos

[ci skip]

* Support increase buffer size

* Add function tests, rename argument

* Update src/Servers/Kestrel/Core/src/Internal/Http3/Http3OutputProducer.cs

Co-authored-by: Stephen Halter <halter73@gmail.com>

* Update src/Servers/Kestrel/Core/src/Internal/Http2/Http2OutputProducer.cs

Co-authored-by: Stephen Halter <halter73@gmail.com>

* Reduce allocations

Co-authored-by: Sebastien Ros <sebastienros@gmail.com>
Co-authored-by: Stephen Halter <halter73@gmail.com>