[wasm] Mark System.Threading APIs as unsupported on Browser

[mdh1418]

Contributes towards #41087

"M:System.Threading.EventWaitHandle.#ctor(System.Boolean,System.Threading.EventResetMode)",System.Threading,EventWaitHandle,".ctor(Boolean, EventResetMode)",2
"M:System.Threading.EventWaitHandle.TryOpenExisting(System.String,System.Threading.EventWaitHandle@)",System.Threading,EventWaitHandle,"TryOpenExisting(String, EventWaitHandle)",1
"M:System.Threading.EventWaitHandle.#ctor(System.Boolean,System.Threading.EventResetMode,System.String)",System.Threading,EventWaitHandle,".ctor(Boolean, EventResetMode, String)",2
"M:System.Threading.EventWaitHandle.#ctor(System.Boolean,System.Threading.EventResetMode,System.String,System.Boolean@)",System.Threading,EventWaitHandle,".ctor(Boolean, EventResetMode, String, Boolean)",1
M:System.Threading.EventWaitHandle.OpenExisting(System.String),System.Threading,EventWaitHandle,OpenExisting(String),1
M:System.Threading.AutoResetEvent.#ctor(System.Boolean),System.Threading,AutoResetEvent,.ctor(Boolean),3
"M:System.Threading.ExecutionContext.GetObjectData(System.Runtime.Serialization.SerializationInfo,System.Runtime.Serialization.StreamingContext)",System.Threading,ExecutionContext,"GetObjectData(SerializationInfo, StreamingContext)",0
M:System.Threading.ManualResetEvent.#ctor(System.Boolean),System.Threading,ManualResetEvent,.ctor(Boolean),3

Marked EventWaitHandle, AutoResetEvent, and ManualResetEvent at class level
Omitted ExecutionContext.GetObjectData as it pertains to Serialization infrastructure

[ghost]

Tagging subscribers to this area: @safern, @ViktorHofer
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[akoeplinger]

These look like false positives. I think the PNSE analyzer got confused by this case which is very uncommon:

runtime/src/mono/netcore/System.Private.CoreLib/src/System/Threading/EventWaitHandle.Unix.Mono.cs

Lines 43 to 44 in 22927dd

	if (name != null)
	throw new PlatformNotSupportedException(SR.PlatformNotSupported_NamedSynchronizationPrimitives);

[mdh1418]

Closing this PR as the relevant changes (EventWaitHandle, AutoResetEvent, and ManualResetEvent) are likely false positives.