Add optional offset argument to StringScanner.peekCodePoint()

[tamcy]

Currently StringScanner.peekChar() accepts an optional argument of offset, but the new StringScanner.peekCodePoint() method doesn't. This PR aims to make StringScanner.peekCodePoint()'s behavior align more with that of StringScanner.peekChar().

This is required if the yaml library is to migrate to string_scanner ^1.2.0 to take advantage from the new codepoint related APIs.

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[tamcy]

Hello, I recommend pausing this pull request. I need to refine my thoughts and will provide an update later.

[tamcy]

Sorry for the late follow up. The reason I asked to pause processing this pull request is that it may bring confusion when an offset
of the peekCodePoint method actually acts upon a code unit, not a code point.

[kevmoo]

Is this needed now?

[lrhn]

I have no problem allowing an offset for peekCodePoint. If you peek ahead and see a non-BMP code point, you should know to increment by two instead of one before doing the next peek.
(That said, I'm not a great fan of the general API here. I'd rather have multiple "cursor objects" on the same input, which can be incremented individually, instead of needing to keep track of integer offsets manually.)

[tamcy]

I am closing it because it isn't needed, at least for now. Thanks for the comment!