traverse_and_serialize_blocks calls is_callable for each block instance

[welcher]

In the traverse_and_serialize_blocks function, the second and third parameters are checked for null for each block in the loop. This check can be done instead once when the function is invoked and cached in variables.

This PR caches the is_callable calls in traverse_and_serialize_blocks rather than calling it for each iteration of the foreach loop. This should improve the performance of the function.

Trac ticket: https://core.trac.wordpress.org/ticket/62063

[welcher]

If this is approved/merged, can we please add Cybr to the props as they brought this to my attention and deserve to share credit.

I did some profiling and found that it reduce total call count for is_callable function and reduce wall time.

Before:

After:

FYI i test TT4 blog page.

[mukesh27]

Introduce in [56644].

Ping @bernhard-reiter for review.

[SergeyBiryukov]

In 59077:

Editor: Optimize is_callable() checks in traverse_and_serialize_blocks().

This aims to improve performance by reducing the number of function calls.

Follow-up to [56644].

Props welcher, Cybr, mukesh27, aristath.
Fixes #62063.

Thanks for the PR! Merged in r59077.