cookie: parse only the exact expire date

The date parser function is very forgiving and skips most "irrelevant"
characters in its hunt for a date to figure out. Therefore it is
impor

cookie: parse only the exact expire date

The date parser function is very forgiving and skips most "irrelevant"
characters in its hunt for a date to figure out. Therefore it is
important to make sure the date string is properly null terminated so
that it does not accidentally parse a piece of whatever text follows
after the date.

Add test483: test (overly) long expire dates in cookies

Closes #15709

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