Initialize RuntimeEventSource as part of coreclr_initialize instead of only when running an app

[elinor-fung]

Fixes #83935

We were only initializing RuntimeEventSource before running an application. This meant that native hosting scenarios - COM, C++/CLI, custom - would never initialize it. As a result, diagnostic tracing tools - like dotnet-counters - did not work properly.

This moves the call to RuntimeEventSource.Initialize out of StartupHookProvider.ManagedStartup and to be part of coreclr_initialize.

Manually validated with dotnet-counters targeting native host and native client for C++/CLI or COM.

cc @dotnet/appmodel

[jkotas]

runtime/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/RuntimeEventSource.cs

Line 56 in 1cc0186

// In CoreCLR, this is done via StartupHookProvider.CoreCLR.cs

should be updated too

[noahfalk]

LGTM!

Also a heads up that the change for #105845 is going to touch some of the same code. You should merge first and I'll rebase around your changes.