Add [RequireStaticDelegate] annotations

[Susko3]

Adds [RequireStaticDelegate] annotation to places where there is an Action<T> + T data overload and the intent is to avoid capture.

Adding this to InvokeOnDisposal is a no-brainer, but I'm not entirely sure about adding to Scheduler and other places. So this is an RFC of sorts.

There are valid use cases of non-static delegates, so I'm thinking it would be useful to apply the attribute, but change the inspection severity to a hint -- let the programmer know that context is captured.
For cases where we want to raise an error for capturing context (eg. in InvokeOnDisposal), [RequireStaticDelegate(IsError = true)] can be used. This will force an error regardless of the configured severity. Unless the severity is configured as DO_NOT_SHOW, in which case the error is silenced.

Example of setting LambdaShouldNotCaptureContext severity to hint. If this is considered too noisy, then we don't apply the attribute in Scheduler, etc.

Inspections that can be configured

LambdaExpressionMustBeStatic

Active when the lambda doesn't capture context, but isn't static.

I think this is best set to hint (defaults to suggestion).

LambdaShouldNotCaptureContext

Active when the lambda captures context (eg. variables, this):

Including when a method is passed and this is implicitly captured:

[smoogipoo]

I like this and I started going down this path with the recent osu-side issues.

I think we should use IsError liberally, including the existing cases in this PR.

[bdach]

I'm not entirely sure about adding to Scheduler and other places

Shouldn't be applied to scheduler at any level higher than a hint at most I think. Using Scheduler.AddOnce() for instance like that has semantics implications.

Also I assume this is going to require game-side changes? Where is that diff?