opt: the get&set way of hashmap using xxhash

[lijinnan123]

I have changed the Chinese to English.

[liuq19]

Thanks, we do not need to open a new pr for this. We can use the previous pr such as #453 , and push all commits into the single branch~

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[liuq19]

We should follow https://github.com/bytedance/sonic/blob/main/CONTRIBUTING.md, pls rename the pr title and reedit the commit msg， such as opt: the get&set way of hashmap using xxhash

Also, please add the xxhash license into licenses/ directory.

[liuq19]

thanks

[liuq19]

Thanks, LGTM

[lijinnan123]

Thanks! Good luck to my teacher!

[liuq19]

Thanks~

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✅ liuq19
❌ lijinnan123
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