coreclr: Automatic port of triple slash from Memory APIs (#2730)

* coreclr: Automatic port of triple slash from Memory APIs

* Update MemoryExtensions.xml

* Some updates.

* Fixed malformed XML

* Fixed bad xrefs

* fixed bad xrefs

* Update MemoryExtensions.xml

* Revised

* Add ## Remarks

* memory ArgumentOutOfRangeException -> memory region

* suggestions by tarekgh

* Fixed malformed XML

* Fixed malformed XML

* Fixed bad paramref tags

Author: carlossanlop