Macro Triggers can't be translated back into ascii codes

[flambard-took]

After #1231, a bug in #859 got exposed. Reported on the forum and discord by Sinclair/ema. Read/writing macro files is completely broken in 1.5.1.

With trigger templates, when the pref file is written (i.e. %, 2) Save file, user-prf.win) the macro triggers are dumped with their human-readable names (\[F1]), not the ascii codes (^_x3B\r).

When such file is loaded, those should be transformed back into ascii, but they actually aren't, due to bug: we are not giving macro_trigger_text_to_ascii() the correct buffer length, we don't actually know the buffer length, because it should come to us as an argument to text_to_ascii call, and that doesn't happen.

In Angband (since at least 3.0.5), text_to_ascii interface accepts the buffer length argument, so I'm just going to use the same fix.