Add preference to disable automatic pen/eraser switching

[SofianElmotiem]

Fixes the annoyance where Openboard auto-switches to the eraser tool when a tablet device (like the Promethean Activ Panel) detects the eraser pointer type. There is now a checkbox in the Pen preferences tab to turn this off. Defaults to on so nothing changes for existing users.

Closes #1432

[Vekhir]

In my opinion, this seems to be a workaround for broken pens. As such, I'd rather the option make that clear with a text like "Ignore broken eraser detection for tablets", defaulting to off. Similar for the variables.

The proper solution would be a driver fix for the pen to disable this behaviour globally, since other software would behave just like OpenBoard. This is far outside the remit of OpenBoard.

[SofianElmotiem]

Thanks for the review! Makes sens
I'll update the label to make it clear this is a workaround, flip the default to off, and rename the variables accordingly.

[Vekhir]

Looks fine now. The commit messages are very structured.

[SofianElmotiem]

Your suggestion made the intent much clearer that i need to rethink about it , and let me know if there is anything else to adjust before this can be merged.

[Vekhir]

Some people like to add a Signed-off-by: to signify that they as a human are the original authors of the code. It's part of the Developer Certificate of Origin.

What do you think?

[SofianElmotiem]

Honsetly did not know it before but for sure happy to add it

[Vekhir]

I saw that your account is quite new, so I thought to mention it.
From this point, I don't have anything else to add. Let's see what the others might say.

[SofianElmotiem]

thats right it took me some time considering contributing to opensource but i did it in the end. so i am happy to share and learn from the community.

[Vekhir]

Welcome to opensource!