Full values of DateTimes should be more accessible

[rbasralian]

It would be helpful if datetime columns had tooltips that showed the complete date and time:

[vbabich]

Needs spec

[mofojed]

Moved the "Copy Cell Unformatted" to it's own ticket #919

[mofojed]

We do tooltips for URLs as a precedent.

from deephaven import empty_table
t = empty_table(100).update("x=`https://www.example.com/` + i")