P2: Flutter tree table should fill screen

[kenzieschmoll]

Example where last column does not extend to right edge of screen

It would also be nice to have some additional padding between the total time and self time columns

[kenzieschmoll]

This is starting to become a larger issue as we add more tables to devtools. We need a more flexible table implementation that does not rely on hard coded px column width values.

[kenzieschmoll]

dupe of #2047