HarfBuzz added support for parsing VORG and VMTX vertical metrics as part of hb_font. We should remove our internal implementation in OpenTypeVerticalMetrics and stop configuring the two vertical metrics related callback functions for HarfBuzz

    hb_font_funcs_set_glyph_v_origin_func(funcs, HarfBuzzGetGlyphVerticalOrigin,
                                          nullptr, nullptr);
    hb_font_funcs_set_glyph_extents_func(funcs, HarfBuzzGetGlyphExtents,
                                         nullptr, nullptr);

However, we have to defer this to past rolling HarfBuzz to support AAT natively, as there are additional issues to be ironed out.

Ad hoc, the list of test cases that shows unexpected results after deleting the function registrations is as follows:

 fast/css3-text/css3-text-decoration/text-decoration-skip-ink.html
 fast/text/font-format-support-color-cff2-vertical.html
 fast/text/justify-ideograph-vertical.html
 fast/text/orientation-sideways.html
 fast/writing-mode/Kusa-Makura-background-canvas.html
 fast/writing-mode/broken-ideograph-small-caps.html
 fast/writing-mode/broken-ideographic-font.html
 fast/writing-mode/japanese-rl-text-with-broken-font.html
 fast/writing-mode/text-orientation-basic.html
 svg/W3C-SVG-1.1/text-align-05-b.svg
 svg/W3C-SVG-1.1/text-align-06-b.svg
 svg/W3C-SVG-1.1/text-intro-03-b.svg
 svg/batik/text/verticalText.svg
 svg/batik/text/verticalTextOnPath.svg
 svg/text/text-selection-align-05-b.svg
 svg/text/text-selection-align-06-b.svg
 virtual/layout_ng/fast/writing-mode/Kusa-Makura-background-canvas.html
 virtual/layout_ng/fast/writing-mode/broken-ideograph-small-caps.html
 virtual/layout_ng/fast/writing-mode/broken-ideographic-font.html
 virtual/layout_ng/fast/writing-mode/japanese-rl-text-with-broken-font.html
 virtual/layout_ng/fast/writing-mode/text-orientation-basic.html
 

Especially the SVG text*align* tests are affected, showing issues with glyph positioning and bounding box calculations: Bounding boxes for adjacent glyphs do not share a boundary but look like they have letter-spacing applied.