bug#51794: 29.0.50; invalid input events generated from a mouse click for the tab bar

[Eli Zaretskii]

> From: Mark Kennedy <mark.t.kennedy@gmail.com>
> Date: Fri, 12 Nov 2021 15:49:45 -0500
> 
> 1) launch an emacs with two windows
> 2) one window has a number of tabs with text files in each
> 3) the other window has at least one tab with a scala source file,
> in scala mode, using LSP
> 4) the emacs instance is configured to use lsp-metals
> 5) clicking on the tabs in the text file window works as expected
> (e.g. selection, closing)
> 6) clicking on a tab in the window with the scala source file triggers
> the message "<nil> <mouse-1> is undefined".
> 7) switching from scala mode to fundamental mode restores the correct
> tab behavior.
> 8) switching back to scala mode from fundamental mode restores the
> failing behavior

Does scala mode rebind mouse clicks to some of its commands?  If so,
please show those rebindings.