Fix form reset for x-model radio, checkbox arrays, select multiple and various modifiers

[bb]

This PR fixes form reset for many input types (radio, checkbox array, select multiple) plain as well as in combination with number and boolean modifiers for casting as well as fill modifier for <select multiple and also fixes duplicated entries with checkbox arrays during reset.

A few tests have been added, all of them were failing before this PR and are good now.

Some of the fixes in more detail:

• Fix form reset for x-model radio inputs.
  • Without this fix, always the value of the last radio input (in the test: radio3) is set to the model.
• Fix form reset for x-model checkbox array inputs.
  • Without this fix, always the value of the last checkbox input (in this test: checkbox4) is set to the model (no matter if it was checked or not).
• Fix form reset for x-model radio inputs with number and boolean modifiers
  • Without this reset would set strings to the model
• Fix form reset for select multiple
• Fix fill for select multiple
• Fix x-model select multiple with number and boolean modifiers
  • Without this reset would set strings to the model

... and possibly a few more.

[bb]

I started out adding more and more conditions in the reset listener but settled on simply always using the getInputValue approach because I basically ended up duplicating all the conditions from there anyway. In between it looked like this:

nextTick(() => el._x_model && (el.type !== 'radio' || el.checked) && (((el.type === 'checkbox' && Array.isArray(getValue())) || el.type === 'radio' || (el.tagName.toLowerCase() === 'select')) ? setValue(getInputValue(el, modifiers, { target: el }, getValue())) : el._x_model.set(el.value)))

now it's just

nextTick(() => el._x_model && el._x_model.set(getInputValue(el, modifiers, { target: el }, getValue())))

I kept using the public setter (which was prepared to allow programmatic overriding of x-model as described in a comment below that line). However, there are some places in the code which do not use the overridable setter: cloning and when using .fill. So I wonder if there are more bugs hidden in this area. I recommend adding a test for overriding the setter to make sure there are none.

[calebporzio]

Thanks @bb! Thanks for all your work on this