Change: Vertically centre sprite font relative to TrueType font.

[PeterN]

Motivation / Problem

Currently we try to draw the sprite font aligned to the base line of the TrueType font, however this has some issues:

1. Individual sprite height is used but y_offs is ignored so sprites are not aligned correctly. This is noticeable with OpenGFX.
2. If the TrueType font is smaller than the sprite font it overflows above the font.
3. Since variable scaling, the sprite font is centred within the scaled font height when not using TrueType fonts.

Description

These are mostly resolved here by:

1. Using the scaled sprite font height rather than individual sprite sizes. Alignment is always correct.
2. & 3. Vertically centring the sprite within the TrueType font's height. This avoids overflowing above the font (it can still overflow, but this will be shared top & bottom), and makes the alignment consistent between TrueType and non-TrueType rendering.

Change when using Liberation Sans size 10 at 2x, old vs new:

Change when using Liberation Sans size 10 at 3x, old vs new:

Change in station label using Liberation Sans size 6 as 2x, old vs new:

(In these screenshots, it is the bus glyph that is incorrectly positioned before this change)

This change also fixes users of static function GetDefaultFontHeight() to call it properly.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker