Align TextBuilder characters by their baselines during addition/removal

[frenzibyte]

Previously characters were implicitly aligned using their YOffsets, and that works when only one font is used, but not when more than one font gets used inside one SpriteText/TextBuilder.

This PR aims to resolve the "multiple fonts" case by offsetting their DrawRectangles based on the difference between the Baseline of the new character and the previous characters.

I've worked on this initially so that font-mixed sprite texts with #3271 don't look badly misaligned (as I noticed after implementing #3271), but apparently, there are already alignment improvements osu!-side with this PR alone (although slightly unnoticable):

• Before:
  

• After:
  

(notice (TV Size) aligned correctly with the other glyphs)

I have added in-depth test coverage in TextBuilderTest which had the perfect setup for having so, with all possible scenarios I can think of.

Along with test coverage, I've also added a benchmark including the regular "no baseline adjustment" cases, and "one baseline adjustment every 10 characters" case, and the results seem reasonable.

Method	Mean	Error	StdDev
AddCharacters	19.99 us	0.280 us	0.323 us
AddCharactersWithDifferentBaselines	31.02 us	0.219 us	0.183 us
RemoveLastCharacter	24.90 us	0.493 us	0.506 us
RemoveLastCharacterWithDifferentBaselines	38.14 us	0.570 us	0.505 us

I can see this being further optimised by offseting new characters to negative X/Ys rather than offsetting all the other previous characters in the line, but that might be a bit complicated to deal with in the SpriteText_DrawNode (especially given that TextBuilder can have multiple lines), therefore I've went with the simplest way of for looping all characters in the line for now.

[smoogipoo]

Looks solid. As I mentioned in discord, we probably want to rework TextBuilder altogether to improve performance - having everything done in-line in AddCharacter/RemoveCharacter is not good, but that goes for everything else as well.

[peppy]

this is missing a breaking change clause for the updated method signature, will add.

[peppy]

Actually there's quite a few changes, just going to leave it. All mostly internal stuff so I don't think too many people will be hit by it.