Date/Time: In `get_the_date()` and related functions, pass the original,...

Date/Time: In `get_the_date()` and related functions, pass the original, unmodified `$format` value to the filters.

Additionally, simplify the `$format` argument checks for consistency with similar checks in `get_the_modified_date()` and `get_the_modified_time()`.

Follow-up to [48912].

Props Rarst.
Merges [48918] to the 5.5 branch.
See #51184.
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git-svn-id: https://core.svn.wordpress.org/branches/5.5@48684 1a063a9b-81f0-0310-95a4-ce76da25c4cd