[3.0] Theme split (wave 4, part 8) — use the shared confirmation handler instead of inline onclick

[albertlast]

Description

Part of the split of #7933, wave 4 part 8.

Four buttons still ask for confirmation with an inline handler, in two spellings:

onclick="return confirm(\'…\');"
onclick="if (!confirm(\'…\')) return false;"

script.js has carried a delegated .you_sure handler for exactly this, and most
of the forum already uses it — the error log, the calendar, the custom profile
field editor, the mark-all-as-read button. This moves the last four over, with the
message in data-confirm as everywhere else.

The shared handler also does something the inline calls do not:

// Check if the browser disabled the alert
if (!result && (timeAfter - timeBefore) < 10)
	return true;

If confirm() comes back false in under ten milliseconds it assumes the dialog
was suppressed by the browser and lets the action through, rather than the button
silently doing nothing. The inline versions have no such fallback.

file	button
PersonalMessage.template.php	delete selected, on the message index and on a conversation
PersonalMessage.template.php	apply rules
ManageLanguages.template.php	delete a language

Testing

Dispatched a real click at each button with window.confirm stubbed, and read
event.defaultPrevented after the delegated handler had run:

button	declined	accepted
PM → delete selected	click blocked	click proceeds
PM → apply rules	click blocked	navigates to …sa=manrules;apply

Both come out with class="button you_sure", the string in data-confirm, and no
onclick left.

Worth noting how that had to be measured: a stub that returns instantly is treated
by the handler as a suppressed dialog and the click goes through anyway. My first
attempt therefore "showed" that declining did nothing. The stub has to take longer
than the ten millisecond threshold before the result means anything.

The language delete button I have not exercised — it only appears once a second
language is installed, and I have one. It is the same one-line swap as the three
above.

Issues References (Fixes|Related|Closes)

Related to #7933