[SR] Expose public API for flutter

[romtsn]

#skip-changelog

📜 Description

• Rework ReplayIntegration so it can accept a Recorder as a parameter and be used in e.g. Flutter by reusing most parts of the replay logic from the native layer
• Make ReplayIntegration testable and add a simple test with a different recorder. This is just a first step to make it testable and cover it with tests

💡 Motivation and Context

Part of getsentry/sentry#63255

💚 How did you test it?

Ivan did

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	363.11 ms	441.60 ms	78.49 ms
Size	1.70 MiB	2.32 MiB	633.47 KiB

Baseline results on branch: rz/feat/session-replay-breadcrumbs

Startup times

Revision	Plain	With Sentry	Diff
40daa25	438.42 ms	513.67 ms	75.25 ms
150dd36	397.04 ms	446.85 ms	49.81 ms

App size

Revision	Plain	With Sentry	Diff
40daa25	1.70 MiB	2.32 MiB	633.29 KiB
150dd36	1.70 MiB	2.32 MiB	633.30 KiB

Previous results on branch: rz/feat/session-replay-public-api

Startup times

Revision	Plain	With Sentry	Diff
a82aaa3	341.67 ms	403.26 ms	61.59 ms

App size

Revision	Plain	With Sentry	Diff
a82aaa3	1.70 MiB	2.32 MiB	633.46 KiB