[Sync-EN] Add examples for filter_var_array() and filter_input_array()

[lacatoire]

Syncs reference/filter/functions/filter-input-array.xml and reference/filter/functions/filter-var-array.xml with php/doc-en#5267 and php/doc-en#5699.

filter_input_array():

• The return value is described accurately: null is returned when the input array is not populated, regardless of FILTER_NULL_ON_FAILURE; missing entries are null when add_empty is true and omitted when it is false, and unlike filter_input() the flag does not change that; with FILTER_FORCE_ARRAY a failure value is wrapped in a one element array like any other result.
• The RU-only example, a leftover from a version of the English page that no longer has it, is replaced by the three upstream examples: filtering GET input with a failing entry, filtering POST data with a missing field, and requesting an input type that is not populated.
• Mirrors the removal of the two empty xi:fallback elements.

filter_var_array():

• The return value section gains the missing-entry and failure-value paragraphs, matching filter_input_array().
• The first example gains the note that entries are filtered as scalars unless FILTER_REQUIRE_ARRAY or FILTER_FORCE_ARRAY is used, so the FILTER_REQUIRE_SCALAR flag in it only states the default explicitly.
• Adds the "single filter for all values" and FILTER_CALLBACK examples.
• Two wording fixes in the options description: the key corresponds to a key in the input array, and 'flags' specifies any flags that apply.

EN-Revision bumped to 85264ba268a398c4b90c1948839d54ce688dd5cd on both files.

Fixes: #1694