test(dom): increase code coverage for input, textarea, and doctype nodes

[pgoldrbx]

Description

• expand test coverage for less common scenarios
• add tests for when input values are set at runtime rather than by initial attribute
• include tests for doctype node

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore, documentation, cleanup

Related Issue

Motivation and Context

This is work to help unblocking the jsdom upgrade by improving overall test coverage #20
There is nothing so far in these tests that gives me any concern about updating jsdom

How Has This Been Tested?

Screenshots (if appropriate):

Checklist:

• My code follows the code style of this project.
• I have updated the documentation (if required).
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 95

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+4.9%) to 69.633%

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Totals
Change from base Build 90:	4.9%
Covered Lines:	287
Relevant Lines:	375

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💛 - Coveralls

[neilius]

👍