Add octave jumps and jumping to notes that exist

Arrowing cell by cell is right inside a dense bar and tedious across an
empty one. Three pairs of keys now jump straight to a note that is really
there, one pair for each axis:

  Alt+Up/Down            the column -- next pitch sounding in this cell
  Alt+Left/Right         the row    -- next note at the cursor's pitch
  Ctrl+Alt+Left/Right    anywhere   -- next note in the take, any pitch

plus Ctrl+Alt+Up/Down for whole-octave movement, which needs no scale
awareness because an octave preserves the pitch class.

All the jumps ignore muted notes, which are not audible content, and the
row and any-note jumps anchor on note starts, so a note held across eight
cells is one stop rather than eight. Landing in a chord takes whichever
note is nearest the pitch you came from rather than always the bottom one.

They sit on Ctrl+Alt rather than plain Ctrl because REAPER already uses
Ctrl+arrows to move between items.

The logic lives in the lib as usual, with four run* drivers following the
runShift pattern, so the eight new action scripts are seven lines each.

test_lib.lua previously dofile'd an absolute D:\ path and so could not run
outside one machine; it now resolves the lib relative to itself. Stubbing
MIDI_GetNote and the PPQ conversions reaches further than the old "pure
logic only" boundary, so the new tests cover the search functions and the
drivers' speech and cursor movement too.

MidiGrid_RowPrev.lua

@@ -0,0 +1,7 @@
+-- MIDI Grid: previous note at this pitch (pass-through when grid mode is off)
+local dir = ({ reaper.get_action_context() })[2]:match("@?(.*[\\/])")
+local G = dofile(dir .. "midigrid_lib.lua")
+
+if not G.isActive() then G.passThrough("_OSARA_PREVCHORD") return end
+
+G.runRowJump(-1)