Update MERP event type to MonoAppCrash (mono/mono#17131)

Update MERP event type to MonoAppCrash (mono/mono#17131)

* Update parameters in MERP WerReportMetadata xml

To enable backend analysis, we need to update our parameters to match our back end event type, which is MonoAppCrash.

It doesn't make sense to me that the previous implementation constructed the XML here in Mono, but depended on the user (VSMac in this case) to add the "correct" event type.  The parameters in the XML, must match exactly what is expected for the given EventType, and so we should ensure they are always in-sync by defining them here.  Thus, I removed the usage of `eventType` in `mono_merp_enable` and hard coded the expected eventType.

* [merp] Don't pass eventType from managed

The eventType must me MONO_MERP_EVENT_TYPE_STR ("MonoAppCrash") - the backend
determines the format of the other fields based on the event type, so it
doesn't make sense to pass other values from managed since the runtime controls
the other fields.

For compatability Mono.Runtime.EnableMicrosoftTelemetry will still take a
string parameter (now called "unused" instead of "eventType_str") but it will
not pass it down to the internal call.

* Bump corlib version

* [merp] Revert paramerters in WerReportMetadata.xml

Still need event type to be `MonoAppCrash` but the parameters will be the same as before.

Commit migrated from https://github.com/mono/mono/commit/481b3005c63daa38d163e46ef5bb43288b1403b7