Enable option to raise exception if magicgui cannot determine widget for provided value/annotation

[Czaki]

This PR adds the option to raise exceptions if magicgui cannot determine a widget or a given type.

By default, the exception is not raised if using magicgui decorator but is raised if create_widget is called directly. Is it OK for you @tlambert03

closes #473

[codecov]

Codecov Report

Merging #476 (e6352a3) into main (9e29739) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #476      +/-   ##
==========================================
+ Coverage   88.08%   88.09%   +0.01%     
==========================================
  Files          31       31              
  Lines        4189     4193       +4     
==========================================
+ Hits         3690     3694       +4     
  Misses        499      499              

Impacted Files	Coverage Δ
magicgui/_magicgui.py	96.29% <ø> (ø)
magicgui/signature.py	96.66% <100.00%> (+0.03%)	⬆️
magicgui/type_map.py	95.72% <100.00%> (+0.04%)	⬆️
magicgui/widgets/_bases/create_widget.py	97.36% <100.00%> (+0.07%)	⬆️
magicgui/widgets/_function_gui.py	94.04% <100.00%> (ø)

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[tlambert03]

yeah, I think this looks good to me. It's a shame this has to go all the way through signature.py and everything... but I took a look and I agree it seems to be the way to do it. (would probably be a bit easier with the pattern proposed in #474 ... but we can just make sure to respect the same intention as whatever you implement here when that is implemented)

let me know when this is ready for final review (could be now?)

[Czaki]

let me know when this is ready for final review (could be now?)

there is no test (i will add) but you could review everything else.

[Czaki]

ready

[tlambert03]

thanks!