Proposal to Improve Performance of `info-apropos` Command in GNU Emacs

[Eval EXEC]

Hello,

I would like to propose an idea to enhance the performance of the 
`info-apropos` command in GNU Emacs. Currently, I have observed that 
`info-apropos` performs searches sequentially, scanning through each node one 
by one, resulting in longer execution times. On my system, for instance, 
executing `M-x info-apropos RET advice-add RET` takes approximately 8 seconds.

To enhance the efficiency of `info-apropos`, I suggest implementing a parallel 
search mechanism that utilizes multiple threads to search through nodes 
simultaneously. This approach has the potential to bring significant 
performance improvements, especially on multi-core CPUs. I believe such 
optimization could potentially result in a 10x speed boost.

I would greatly appreciate it if you could consider this idea for improving the 
`info-apropos` command. Please let me know your thoughts and if you require any 
additional information.


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