[IMP] spreadsheet: mark _t function to be hidden

This commits hides a function in spreadsheet that are not supposed to be
used by end users: `_t`. It can only work with static strings in the source
code.

task 3102309

closes odoo/odoo#109863

Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>

addons/spreadsheet/static/src/o_spreadsheet/translation.js

@@ -13,4 +13,5 @@ functionRegistry.add("_t", {
         return _t(toString(value));
     },
     returns: ["STRING"],
+    hidden: true,
 });