Polish the UI for size profiles enough to be comfortable enabling it by default on the Firefox JSON Viewer

[fqueze]

Known issues:

• the interval in the profile info panel is shown with a time unit.
• the stack chart tooltips show time units (but the flame graph tooltips show correct size units!)
• the CPU percentage line in the timeline tooltip doesn't make much sense.
• the 'Call Tree' panel name doesn't make sense for a file size (and the 'Stack Chart' name might not be great either).

More generally applicable issues that were mentioned in the JSON size profiler review:

• The track selector is still there for profiles with a single track
• The empty 'Marker Chart' and 'Marker Table' panels should be hidden for profiles without markers.

┆Issue is synchronized with this Jira Task

[fqueze]

I opened #5656, #5657 and #5658, I'll wait for reviews before doing more changes for this.