[ASEditableTextNode] Round up editable text node to the next point

[vadims]

Rounding up to the next device pixel was calculating a height smaller
than UITextView's contentSize. This was causing the baseline to move as
the user was typing.

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[appleguy]

Solution to #1760

[appleguy]

@vadims thanks for fixing this! I'm pretty annoyed by the name of ceilSizeValue - it is not at all clear that it does screen pixel rounding rather than points (e.g. numerical rounding).

@vadims / @maicki it would be nice to include a short comment here clarifying that it is important to use points / UITextView apparently does sizing on a whole-point basis. We should also rename the other method to more clearly describe its scale-dependent behavior.