Add session replay assertions for internal testing

[louiszawadzki]

What does this PR do?

Adds assertions for the Session Replay events.
For now we only assert on full snapshots, but that's enough to make sure the custom mappers we've added for RN session replay are working as intented.

For Android we had to add a bunch of improvements:

• the detected padding was 1px off sometimes, so I added some flexibility into the assertions for padding
• the default color was #0 instead of #000000FF, so I fixed it
• the color was in lowercase vs uppercase for iOS, I formatted all colors to be uppercase

Motivation

Being able to run UI-level tests to better cover the Session Replay feature.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[0xnm]

I didn't dig too much into TS/Swift code, but Kotlin part lgtm.

[0xnm]

if it is not set, won't resolvedColor below be null? if it is the case, we can probably simply return #000000FF there directly, without querying another property here

[louiszawadzki]

If it is not set resolvedColor will actually return 0. It will return null if for some reason it cannot get access to the property through reflection