feat(linux): comments on module u16 🐘

[SabineSIL]

fixes parts of PR https://github.com/keymanapp/keyman/pull/9384. Some comments may have been moved into an issue https://github.com/keymanapp/keyman/issues/11802

This PR addresses and bundles comments made on https://github.com/keymanapp/keyman/pull/9384 for the module u16

double function misleading name sz naming save c_str() call start with /0 wrong comment naming remove ToHex remove comments

unit tests @keymanapp-test-bot skip

[keymanapp-test-bot[bot]]

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