use TypeDescriptor.forObject instead of constructor; enforce use of TypeDescriptor.valueOf through making the constructor private

ObjectToObject converter now only matches public methods/constructors; private class method invocations also supported now through a makeAccessible call

catch ConversionException and ConvertedNotFoundException in BeanWrapper's convertIfNecessary as well, in order to support constructor resolution (SPR-6563)

introspect element type in case of incoming Collection/Map in order to not accidentally say canConvert=true (SPR-6564)

rearranged spel subpackages in order to avoid package dependency cycle; introduced SpelParserConfiguration object to replace bit flags

added special handling of String array values for required fields, e.g. for WebRequestDataBinder (SPR-6552)