Preserve the System.RuntimeType constructor in mono ILLink

[tannergooding]

Fixes #48522

Without this, the linker will think that RuntimeType is never instantiated and can generate code such as (the red without this fix vs the green with this fix):

-      Type underlyingSystemType = type.UnderlyingSystemType;
-      RuntimeType runtimeType = (RuntimeType) null;
-      if ((object) runtimeType != null)
-        return runtimeType.CreateInstanceImpl(bindingAttr, binder, args, culture);
+      RuntimeType underlyingSystemType = type.UnderlyingSystemType as RuntimeType;
+      if ((object) underlyingSystemType != null)
+        return underlyingSystemType.CreateInstanceImpl(bindingAttr, binder, args, culture);

Additionally, under this scenario the runtime will end up failing to load S.P.Corelib with an error similar to:

WASM-ERR: [ERROR] FATAL UNHANDLED EXCEPTION: Nested exception detected.
WASM-ERR: Original Exception: at System.Collections.Generic.Dictionary`2<string, object>..ctor (int,System.Collections.Generic.IEqualityComparer`1<string>) <0x00060>
WASM-ERR: at System.Collections.Generic.Dictionary`2<string, object>..ctor (int) <0x00014>
WASM-ERR: at System.AppContext.Setup (char**,char**,int) <0x00016>
WASM-ERR:
WASM-ERR: Nested exception:at System.RuntimeType.get_BaseType () <0x00056>
WASM-ERR: at System.Type.IsSubclassOf (System.Type) <0x00044>
WASM-ERR: at System.Reflection.CustomAttribute.IsDefined (System.Reflection.ICustomAttributeProvider,System.Type,bool) <0x00040>
WASM-ERR: at System.Reflection.RuntimeMethodInfo.IsDefined (System.Type,bool) <0x00016>
WASM-ERR: at System.Diagnostics.StackTrace.ShowInStackTrace (System.Reflection.MethodBase) <0x00048>
WASM-ERR: at System.Diagnostics.StackTrace.ToString (System.Diagnostics.StackTrace/TraceFormat,System.Text.StringBuilder) <0x000c8>
WASM-ERR: at System.Diagnostics.StackTrace.ToString (System.Diagnostics.StackTrace/TraceFormat) <0x00036>
WASM-ERR: at System.Exception.GetStackTrace (bool) <0x0006a>
WASM-ERR: at System.Exception.get_StackTrace () <0x0000e>
WASM-ERR: at System.Exception.ToString () <0x000ae>
WASM-ERR: at System.Exception.ToString () <0x00054>
WASM-ERR:
WASM-ERR:

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[tannergooding]

CC. @eerhardt

[eerhardt]

I think this might fix #48522

[joperezr]

I think this might fix #48522

Confirmed, just ran the tests with this change and without the workaround I added and all test pass for browser-wasm. I'll take the liberty to modify the PR description to add the fixes message.

[lewing]

Thanks for tracking this down @tannergooding

[eerhardt]

Looks good to me. I'm super happy you were able to trace this down. Nice work.

[ghost]

Hello @tannergooding!

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[joperezr]

The failure in the dotnet-liner-tests pipeline is a race condition that I'm already fixing on my PR #48429 so feel free to disregard that