docs: corrected "MB_LEN_MAX" description

[spacemiqote]

I updated the description of MB_LEN_MAX to better align with the documentation from the Microsoft C Runtime Library.
For more details, please refer to: https://github.com/MicrosoftDocs/cpp-docs/blob/main/docs/c-runtime-library/data-type-constants.md
Best regards,

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[TylerMSFT]

Thank you! Appreciate you touching up the docs here.