Universal non-integer note tone (for microtonal and different musical tunings like Just intonation)

[oxygen-dioxide]

This issue was brought up several times here:

• No note-level pitch #812
• https://discord.com/channels/551606189386104834/1132547576126787675/1132547576126787675

One solution is using t flag. However, flags work for each phoneme instead of each note. If you have a group of slur notes, you can't specify a different t flag for each note inside it. For VCV voicebanks, the t flag will affect the tail part of the previous note, and there will be phase issue if it has a different t flag from the previous note. Besides, it is only supported by certain resamplers. Worldline, worldline-R, vogen, NNSVS and diffsinger don't support it.

Another solution is manually adjusting the pitch control points or the hand-drawn pitch line. However, adjusting the pitch curve for each note is a hassle.

If we need to resolve this problem completely, I think we should have a universal non-integer note tone support in OpenUtau. The note will still snap to integer tone by default. Users can shift-drag the note to adjust its tone by cents, and the default pitch control points of this note will go with the tone. ML-generated pitch curves (such as diffsinger) will also use this non-integer tone as input.