[wasm] Standup EnableAgressiveTrimming for library tests (#46367)

[wasm] Standup EnableAgressiveTrimming for library tests (#46367)

* Trim wasm library tests

* Add SystemBuffers HelloTest and only test that

* Import linker from nuget to override sdk linker

* Remove redundant assembly inclusions

* Add WasmTestRunner referenced assemblies

* Add properties to reduce library size

* Updates

* Configure trimming for library tests

* Link assemblies except for test assembly

* Use another path to WasmTestRunner.dll

* Fix typo

* Setup correctly rooted assemblies

* Don't copy WasmTestRunner.dll from wrong patch when using linker

* Don't inflate publish output with packages which are not used for tests runs

* Fix xunit framework files copying to publish location to not overwrite
version copied as part of trimming publish

* Add linker descriptor for xunit code which linker cannot track

* Add tested assembly to the test payload closure

* One more method to preserve

* Preserving some xunit types to make sure we can actually discover the tests

* Put Wasm.targets import in the right spot

* Add a mode where we can run the regular system.buffers tests

* Dont link out Microsoft.DotNet.RemoteExecutor

* Move Microsoft.DotNet.RemoteExecutor inclusion to xml

* Consolidate ConfigureTrimming itemgroups

* Build PrepareForWasmBuildApp before WasmBuildApp

* Remove manual import of WasmTestRunner assemblies

* Remove temporary HelloTest from System.Buffers

* Added flag to not aggressively link by default

* Revert import and build order changes

* Condition trimming related changes on EnableAggressiveTrimming

* Revert "Don't copy WasmTestRunner.dll from wrong patch when using linker" as MainAssembly is back to $(PublishDir)\WasmTestRunner.dll
This reverts commit 79dc240f4c99f61af1a7e4c98d299be25f8f854e.

* Add comment to note temporary RemoteExecutor assembly inclusion

* Move props from general tests to mobile tests

* Revert "Condition trimming related changes on EnableAggressiveTrimming"

This reverts commit a97fb56eeb47522a4af1e7e47acd3595cf48271e.

* Broaden trimming options for all mobile targets

* Enable PublishTrimmed regardless of OS when aggressively trimming

* Move trimming specific property to ConfigureTrimming

* Import NuGet linker in mobile tests by default

* Add file description

* Add detail to ILLink XML descriptor file

* Reformat ConfigureTrimming target tag

* Fix typo

Co-authored-by: Mitchell Hwang <mitchell.hwang@microsoft.com>
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
Co-authored-by: Marek Safar <marek.safar@gmail.com>