Fix character, underline and strikethrough drawing over label boundary for Overflow::CLAMP mode

[rh101]

Describe your changes

Ensure that underline and strike-through lines are clamped correctly when overflow is set to Overflow::CLAMP

This also fixes the issue of characters being drawn over the label boundary when using Overflow::CLAMP.

Label tests 56 and 57 cover this in the cpp-tests project.

Issue ticket number and link

#2513
#2516

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[aismann]

For backwards compatilibty and "no API change":
bool isHorizontalClamped(float letterPositionX, int lineIndex, float letterWidth = 0);

[rh101]

For backwards compatilibty and "no API change": bool isHorizontalClamped(float letterPositionX, int lineIndex, float letterWidth = 0);

There is no change to the API, since the method is not virtual, and also not part of the public API, so it will not be called outside of Label.

If update it regardless of that, but it really is unnecessary.
Actually, letterWidth cannot be set to 0 as default, since that would not behave as it did previously, so it must remain as-is. There is no API change, so it's a non-issue.