Thoughts on the "Direction" property for text elements

One of features I am most looking forward to having available in MuseScore 3 is the new "Direction" property for text elements. This allows them to easily be flipped above or below the staff, just like we do for articulations, slurs, ties, etc (hmm, what else?)

However, it seems that right now the feature is a bit more limited than I would prefer. My concerns are:

1) the effect of flipping seems to assume a five-line staff with default spacing
2) no way to specify different default vertical alignments & offset for above versus below
3) no way to specify a default direction for a given text style

By 1), I mean, if you flip a text from above to below the staff, it's too far below for 1-line or 3-line percussion staves, not far enough below for 6-line tab staves:

By 2), I mean, you might want things set up to that when text is above, the bottom/baseline of the text is 2sp above the staff, but when below, chances are good we really want the *top* of the text to be 2sp below the staff, so either way there is 2sp clearance. If so, you'd probably want to be able to say, use bottom/baseline alignment when above, use top alignment when below. But maybe you care more about making sure the text aligns well when placed below the staff, so you want to use baseline alignment in either case, but you want to set it so that baseline is 2sp above the staff but maybe 3sp below, so the clearance is approximately 2sp either way but aligns well. Or, maybe you actually want it so that when above the staff, you want *more* clearance (or less) than when below. For example, maybe you want dynamics for vocal staves to be slightly above the staff by default, but when flipped below, have them *way* below so they clear the lyrics.

We could solve this with additional fields in the text style, but maybe MuseScore should just do the calculation itself to provide a more reasonable default. Currently, it seems that MuseScore basically just adds 5sp to the offset when flipping text from above to below, and also silently converts to bottom alignment:

I think it should convert top alignment to bottom and bottom to top, but keep baseline or middle alignment as is (so in the above example, the text would sit directly on the bottom staff line). But it should *also* account for the nominal text height so the effect is more balanced:

Of course, you wouldn't normally normally use 0sp offset for text, but the idea is, the offset then becomes "distance from staff". If you specify a default of -2sp offset with bottom alignment, you get literally 2sp clearance between the bottom of the text and the top of the staff, or when flipped below, you get literally 2sp clearance between the top of the text and the bottom of the staff:

This doesn't directly address the possible desire to have *different* clearance above/below, but maybe that's not so important right now (particularly if collision avoidance reduces the need for this).

There is also some weirdness going on where if you change the alignment in text properties nothing appears to happen - the alignment is changed but the offset is "corrected" to keep the same position, more or less. Maybe that's design, not sure, but it seems glitchy at best. I won't worry about that for now, but I guess it is possible this behavior is confusing me regarding the direction as well and things asre somehow more logical than they appear.

By 3), I mean, if you have a text style you want to default to being below the staff, you shouldn't have to specify a large position offset from the top of the staff. Besides being awkward, it makes the position depend on the staff height, which leads to the complaints we currently get about the default position of dynamics relative to percussion or tab staves:

Instead, we should allow the text style itself to specify whether the default direction is above or below. That way we can have the default for dynamics be 3sp below instead of 8sp "above". 8sp below is only reaosnable for 5-line staves with standard spacing; 3sp below would always be 3sp below.