🐛 incorrect type for context in beforeSend

[thumbsupep]

Describe the bug
With the addition of handlingStack on the context in beforeSend, I am getting a typescript error trying to access it.

To Reproduce
Steps to reproduce the behavior:

1. npm install latest @datadog/browser-rum
2. Implement beforeSend in a typescript file
3. attempt to access context.handlingStack
4. See typescript error

Property 'handlingStack' does not exist on type 'RumActionEventDomainContext | RumFetchResourceEventDomainContext | RumXhrResourceEventDomainContext | RumOtherResourceEventDomainContext | RumErrorEventDomainContext | RumLongTaskEventDomainContext | RumVitalEventDomainContext'.

Expected behavior
No typescript error occurs when trying to access handlingStack

I understand that handlingStack does not exist on some rum event types, but for the ones where it does exist, I should be able to access that property without typescript errors.

I have tried a workaround to create a custom type that I can cast to when accessing handlingStack like so

type RumEventContextWithHandlingStack = Exclude<
  RumEventDomainContext,
  RumViewEventDomainContext | RumOtherResourceEventDomainContext
>;

but there are other types I would need to exclude that are only internal types.

[BenoitZugmeyer]

Thank you for your feedback. Before attempting to access handlingStack, you should do if ('handlingStack' in context). This is a TypeScript limitation, but maybe we could improve the developer experience by making the type less strict ... Instead of having:

type RumEventDomainContext = { handlingStack: string, ... } | { performanceEntry: PerformanceEntry, ... }

we could have optional properties:

type RumEventDomainContext = { handlingStack?: string, performanceEntry?: PerformanceEntry, ...}

I'll chat with the team, but in the meantime, please use if ('handlingStack' in context)