esp-hal: rmt: make ChannelCreator public

[liebman]

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Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
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Pull Request Details 📖

Description

When using an Rmt channel you access rmt.channel0 to grab channel 0. However its type ChannelCreator<> is not public and can't be named as a function arg or struct member. This PR makes that public.

Testing

Compiled/Run in a local project where I add the rmt channels as struct members.

[bjoernQ]

LGTM

[jessebraham]

(Sorry I didn't mean to click that button, can't believe there's no confirmation, hopefully I didn't break anything 🤣)

[JurajSadel]

LGTM, thanks!

[jessebraham]

Thanks!