fix(input): correctly handle invalid model values for input[date/time/…]

Similar to `input[number]` Angular will throw if the model value
for a `input[date]` is not a `Date` object.
For `Invalid Date`s (dates whose `getTime()` is `NaN`) `input[date]`
will render an empty string.

Closes #8949
Closes #9375

docs/content/error/ngModel/datefmt.ngdoc

@@ -0,0 +1,11 @@
+@ngdoc error
+@name ngModel:datefmt
+@fullName Model is not a date object
+@description
+
+All date-related inputs like `<input type="date">` require the model to be a `Date` object.
+If the model is something else, this error will be thrown.
+Angular does not set validation errors on the `<input>` in this case
+as those errors are shown to the user, but the erroneous state was
+caused by incorrect application logic and not by the user.
+