Allow aria-invalid on any element

[missilev]

Closes #252

What:
This PR allows checking if any element is valid, not only on form elements.

Why:
Regarding #252 we need to provide a possibility to check the validity of the element even it's not a form element.

How:
I adapted isElementInvalid function to conditionally call checkValidity if element supports it.

Checklist:

• Documentation
• Tests
• Updated Type Definitions
• Ready to be merged

[codecov]

Codecov Report

Merging #259 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #259   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines          309       313    +4     
  Branches        73        73           
=========================================
+ Hits           309       313    +4     

Impacted Files	Coverage Δ
src/to-be-invalid.js	100.00% <100.00%> (ø)

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@all-contributors add @missilev for code, test

[allcontributors]

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🎉 This PR is included in version 5.10.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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