Some links in the `MessagesView` are part of Element X itself,
such as the help pages in `LearnMoreConfig` [1]. These links
should open in an "in-app" Chrome Custom Tab, because they are
basically part of the app.
Web links from chat messages, on the other hand, should open in
the user's preferred web browser as regular tabs.
Separate "regular" links from "custom tab" links with a new
parameter `onLinkClick(..., customTab)`. If true, the link
opens in a custom tab.
Links within `TimelineView` are always opened in a normal tab.
[1]: appconfig/src/main/kotlin/io/element/android/appconfig/LearnMoreConfig.kt
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