feat(tracing): Move registerErrorInstrumentation to @sentry/core

[timfish]

addTracingExtensions in @sentry/core feels like our better named replacement for addExtensionMethods however it didn't end up with the same functionality.

While working on other tracing PRs I realised that we'd not moved registerErrorInstrumentation to core and it makes more sense for it to be there.

This PR moves registerErrorInstrumentation to @sentry/core and calls it from addTracingExtensions since they are called together in addExtensionMethods. It also adds a flag so errors are only instrumented once. This means we can safely call addTracingExtensions as many times as we like (ie. from integration constructors, etc).

[jensbodal]

I can't find this information elsewhere, does this mean addExtensionMethods is deprecated in favor of addTracingExtensions? The packages only tells me that addExtensionMethods is deprecated but I don't see it exported anywhere else.

[timfish]

The @sentry/tracing package has been deprecated and will be removed in v8.

addTracingExtensions should be exported from every SDK package and should be used as a replacement for addExtensionMethods.

[timfish]

Sorry about that. It looks like this was missed from the migration guide.

I've opened a PR to rectify this!