Replay: method to extract replayId from SDK

[pckilgore]

Problem Statement

Replay urls are nice to automatically attach to out-of-band support events.

It doesn't seem like there's any way to create them with the SDK though, without reading private fields.

Solution Brainstorm

Do what fullstory does with a getReplayURL ability.

#7794

[JoshFerge]

@getsentry/replay-sdk