bug#47012: xref copies keymap properties to minibuffer

[Juri Linkov]

0. emacs -Q
1. C-x p g expose_frame RET
2. put point e.g. on "tab_bar_window"
3. C-x p g M-n
4. click mouse on the default value

Instead of moving point to the clicked position, it visits the xref hit.
This is because the copied default value is not stripped from the
text property 'keymap'.

I noticed this problem after adding RET binding to xref--button-map,
so typing RET on the default value doesn't accept it for new search,
but uses its local keymap to visit old reference.