Create UI Event Transaction for Scrolls, Swipes and other gestures

[bruno-garcia]

Problem Statement

This is a follow up of the UI Event Transaction for Clicks feature added #1784

General SDK tracking issue:

• UI Event Transactions - iOS and Android team-mobile#4

SDK Spec is to be created following:

• Document UI Event Transaction develop#647

[philipphofmann]

When implementing scrolls, please consider adding the performance test as described in #2841.

[philipphofmann]

With single-span ingestion around the corner, we shouldn't create UI event transactions anymore. Instead, we should ingest spans directly for these events, but we still need to come up with a proper concept.