Add equivalent of "hover" for touch displays

**What is the current behaviour and why should it be changed?**

On desktop builds, hovering the mouse over the channel user displays their profile details in a tool tip:

As no "hover" action is available for touch displays (e.g. Android), this feature is unavailable.

**Describe possible approaches**

A single tap or, probably better, long-hold could be used to display tool tips in general. (Long-hold would avoid misinterpretation of single tap on a checkbox or menu, etc.)

I'm guessing touch screens also are missing right-click "What's this?" support. Possibly that could be implemented as above, with "Show musician profile" as an extra option where applicable.

Other trigger actions could be double tap or two-finger tap. Long-hold is prefered, I think.

**Has this feature been discussed and generally agreed?**

Only with my partner, who raised it.

Start by locating the desktop hover tooltip for channel users and the right-click "What's this?" behavior, then inspect how touch input is handled. The issue needs an agreed gesture and should be considered done when touch displays the relevant tooltip or musician profile without misinterpreting taps on controls.

Written by the indexing model from the issue text.