Fix #25299: Allow navigating to grace notes when inputting fingerings

[kennysiucho]

Resolves: #25299

If there are other grace notes (Chords) in the current group, navigate to those first before going to other non-grace chords.

Also restructured some of the other logic to make it more readable.

Added Chord::allGraceChordsOfMainChord() to return the list of grace and non-grace Chords in the current group. I'm also working on fixing grace note navigation using Alt-arrow keys, so this function will come in useful later.

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[mathesoncalum]

Thanks for this @kennysiucho - I've highlighted a couple of bits.

How does it look from an accessibility standpoint @shoogle?

[mathesoncalum]

Suggested change

	GraceNotesGroup gnBefore = mainChord->graceNotesBefore();
	GraceNotesGroup gnAfter = mainChord->graceNotesAfter();
	const GraceNotesGroup& gnBefore = mainChord->graceNotesBefore();
	const GraceNotesGroup& gnAfter = mainChord->graceNotesAfter();

[mathesoncalum]

Suggested change

	std::vector<Chord*> chordList = ch->allGraceChordsOfMainChord();
	const std::vector<Chord*> chordList = ch->allGraceChordsOfMainChord();

[mathesoncalum]

We can make this more concise with some std methods:

Suggested change

	if (!el && ch != (back ? chordList.front() : chordList.back())) {
	for (auto it = chordList.begin(); it != chordList.end(); ++it) {
	if (*it == ch) {
	Chord* targetChord = back ? *(it - 1) : *(it + 1);
	el = back ? targetChord->notes().front() : targetChord->notes().back();
	break;
	}
	}
	}
	if (!el && ch != (back ? chordList.front() : chordList.back())) {
	auto it = std::find(chordList.begin(), chordList.end(), ch);
	if (it != chordList.end()) {
	const Chord* targetChord = back ? *std::prev(it) : *std::next(it);
	el = back ? targetChord->notes().front() : targetChord->notes().back();
	}
	}

...
Arguably it would be a bit more readable if we swapped those final ternary operators with a simple if/else - the tradeoff is that the nesting gets a bit painful. I'll leave it up to you:

if (back) {
    const Chord* targetChord = *std::prev(it);
    el = targetChord->notes().front();
} else {
    const Chord* targetChord = *std::next(it);
    el = targetChord->notes().back();
}

...
As a general note, if this method gets any more complicated I think we should consider splitting it up into lambdas or helpers. Early returns would help a lot with readability here.