(bug 40585) Don't drop 'step="any"' in HTML input fields.

The default value for "step" is "1" which effectively bans any decimal
number from being entered into an 'type="number"' field and makes
HTMLFloatField unusable.

This is a backport of 6dc4039270af99413cc7c3bf85b136d9a79e7497.

Change-Id: Ibda2b49395705c5902c751525b75213653b0ea5d
Merge "(bug 40585) Don't drop 'step="any"' in HTML input fields." into REL1_20