Consider tracking JSON path while deserializing JsonElement to return better JsonException

[ahsonkhan]

We should only do this if it doesn't regress JsonElement performance noticably.

runtime/src/libraries/System.Text.Json/tests/Serialization/ExceptionTests.cs

Lines 366 to 380 in d4b06b1

	[Fact]
	[ActiveIssue("JsonElement needs to support Path")]
	public static void ExtensionPropertyRoundTripFails()
	{
	try
	{
	JsonSerializer.Deserialize<ClassWithExtensionProperty>(@"{""MyNestedClass"":{""UnknownProperty"":bad}}");
	Assert.True(false, "Expected JsonException was not thrown.");
	}
	catch (JsonException e)
	{
	// Until JsonElement supports populating Path ("UnknownProperty"), which will be prepended by the serializer ("MyNestedClass"), this will fail.
	Assert.Equal("$.MyNestedClass.UnknownProperty", e.Path);
	}
	}

cc @steveharter

[layomia]

Closing as duplicate of #29715.