Highlight current format in player's Use Format drop-down menu

**Is your feature request related to a usage problem (not a bug)? Please describe.**
It's not as obvious with some videos to know which mode (audio, legacy or dash) is being used: for instance if the video is showing a picture as it's generally the case for music. The drop-down menu for changing format below the currently playing video doesn't indicate what format is currently being used.

**Describe the solution you'd like to see implemented**
Just like player's video quality setting, highlight the current mode in the drop-down list (see 1st screenshot)

**Describe alternatives you've considered**
Use the same kind of drop-down as in the settings (see 2nd screenshot)

**Screenshots**

**Additional context**
Useless if #1091 is implemented