Ref Assembly and Units for Span.Trim (dotnet/corefx#35576)

Ref Assembly and Units for Span.Trim (dotnet/corefx#35576)

* Units for Trim

* Add ref assembly

* Bug

* Add char units

* Bugs

* CR fixes - 1

* CR fixes - 2

* CR fixes - 3

* CR fixes - 4

* CR fixes - 5

* Revert formatting

* unfo formatting

* Get MemberData working

* Normalize ref

* Manual revert changes

* CR fixes

* Undo code cleanup

* Fixes

* Update ref

* Update ref

* Update ref

* Move memory tests

* Revert StringTests

* Remove redundant unit code

* Add missing refs

* Bug

* dotnet msbuild /t:GenerateReferenceSource

* Revert unintended changes

* POC : Check if fix works

* Fix units

* Revert temp test

* Update ApiCompatBaseline.uapaot.txt

Commit migrated from https://github.com/dotnet/corefx/commit/2191763a765654710df5317dc65dc7cd935bc8c1