minor #10821 Added the missing provided functions (zspine)

This PR was merged into the 3.4 branch.

Discussion
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Added the missing provided functions

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Commits
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71702dd Added the missing provided functions

Author: javiereguiluz

components/polyfill_php73.rst

@@ -30,3 +30,6 @@ Provided Functions
 ~~~~~~~~~~~~~~~~~~
 
 * :phpfunction:`is_countable`
+* :phpfunction:`hrtime`
+* :phpfunction:`array_key_first`
+* :phpfunction:`array_key_last`