Surgical reapply of the surviving half of PR #43517 by @jingsong-liu
(the branch predates the ts-ify migration; its other half — zoom restore
after reload/navigation — landed via #66989).
On US layouts Plus is physically Shift+=, so Cmd+Plus arrives with the
shift modifier set. The blanket 'input.shift' early-return in
installZoomShortcuts silently swallowed keyboard zoom-in on macOS: the
chord matched neither branch and fell through to nothing. Shift is now
evaluated per-chord: zoom-in accepts it, zoom-reset and zoom-out still
reject it (Ctrl/Cmd+Shift+0 and Shift+'-' are different chords).
jingsong-liu
bf39103087