Make vnode.domSize assignment consistent between create and update.

[kfule]

This PR makes the code and behavior of create and update processes more consistent.

Description

• vnode.domSize in updateFragment is now always set to an integer and not left undefined.
  • In createFragment, vnode.domSize is always an integer (temp.childNodes.length), so updateFragment follows it.
  • Accordingly, checks for vnode.domSize === 1 have been added to moveDOM and removeDOM.
• vnode.domSize and vnode.dom assignment code in createComponent and updateComponent are now consistent.

The behavior remains unchanged except that vnode.domSize, which was intentionally undefined, will now be set to 1.
npm run test passes as is.

Also, unnecessary a comment immediately after vnode.domSize in createHTML has been removed as well.

Motivation and Context

This PR fixes inconsistencies in domSize for the following create and update processes:

var comp = {
  view: () =>  m.fragment(m("div"))
}

// create
var v1 = m(comp)
m.render(document.body, v1)
console.log(v1.domSize)          // 1
console.log(v1.instance.domSize) // 1

// update
var v2 = m(comp)
m.render(document.body, v2)
console.log(v2.domSize)          // undefined
console.log(v2.instance.domSize) // undefined

flems

For component vnodes, the code was redundant in both create and update, so I made it simpler and consistent.
Also, the bundle size becomes 8,952 bytes gzipped.

How Has This Been Tested?

npm run test

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)

Checklist

• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires a documentation update, and I've opened a pull request to update it already:
• I have read https://mithril.js.org/contributing.html.

[dead-claudia]

Could you add new tests to verify this behavior? It's clearly a bug fix, so I'd like tests to make sure it doesn't regress further.

[kfule]

@dead-claudia Thank you for your review.
It looks like the existing tests avoided cases where domSize is 1, so I’ve added assertions for those to the existing test cases. I also added checks for other domSize values to keep things consistent with the surrounding code.
Does this look okay to you?

Edit: I also added test cases for consistency of vnode.domSize regarding component vnodes.