Log parsed segment timestamps ahead of append

[robwalch]

This PR will...

• Add fragment "Parsed" log line that reports start and end PTS before append
• Add frag.start and frag.end to fragment "Loading" log lines
• Make fragment Loading > Loaded > Parsed > Buffered log lines more consistent

Why is this Pull Request needed?

This will help in cases where appends fail as well as make it easier to find all lines relevant to a particular segment ("main" or "audio" sn of "level" or "track").

[log] > [stream-controller]: Loading main sn: 4 of level 17 (frag:[23.650-31.533]) cc: 0 [1-77], target: 23.65
[log] > [stream-controller]: Loaded main sn: 4 of level 17
[log] > [stream-controller]: Parsed main sn: 4 of level 17 (frag:[23.650-31.533])
[log] > [stream-controller]: Buffered main sn: 4 of level 17 (frag:[23.650-31.533] > buffer:[0.000-31.533])

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Related to #6191

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md