Reviewed by Darin Adler.

        Refactor parsing/serialization functions in HTMLInputElement.
        https://bugs.webkit.org/show_bug.cgi?id=34852

        - Rename formStringToDouble() to parseToDoubleForNumberType()
        - Rename formStringToDateComponents() to parseToDateComponents()
        - Rename formStringFromDouble() to serializeForNumberType()
        - Add serializeForDateTimeTypes()
          The code is moved from setValueAsDate() and setDateValue().
        - Add serialize()

        parseToDouble() is the top-level function to parse a
        type-dependent string and return a double
        value. parseToDoubleForNumber() and parseToDateComponents()
        functions are helper functions for it. serialize() is the
        top-level function to serialize a double value to a type-dependent
        string, and serializeForNumberType() and
        serializeForDateTimeTypes() are helper functions for it.

        No tests because of no functional changes.

        * html/HTMLInputElement.cpp:
        (WebCore::HTMLInputElement::stepMismatch):
        (WebCore::HTMLInputElement::getAllowedValueStep):
        (WebCore::HTMLInputElement::parseToDouble):
        (WebCore::HTMLInputElement::valueAsDate):
        (WebCore::HTMLInputElement::setValueAsDate):
        (WebCore::HTMLInputElement::setValueAsNumber):
        (WebCore::HTMLInputElement::serializeForDateTimeTypes):
        (WebCore::HTMLInputElement::serialize):
        (WebCore::HTMLInputElement::serializeForNumberType):
        (WebCore::HTMLInputElement::parseToDoubleForNumberType):
        (WebCore::HTMLInputElement::parseToDateComponents):
        * html/HTMLInputElement.h:
        * html/ValidityState.cpp:
        (WebCore::ValidityState::typeMismatch):
        * rendering/RenderSlider.cpp:
        (WebCore::SliderRange::valueFromElement):
        (WebCore::RenderSlider::updateFromElement):
        (WebCore::RenderSlider::setValueForPosition):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54754 268f45cc-cd09-0410-ab3c-d52691b4dbfc