Implement a11y api changes

[zepumph]

These changes where discussed in #686, and decided on in a11y dev meeting today.

• Remove *AsHTML methods and have a single method determine if we should use innerHTML settings or textContent on DOM elements. Performance considerations in the comment [Discussion] Rethink cases for setAccessibleContent #686 (comment)

• Reimplement accessibleLabel: {{string}} so that it only ever set's a sibling DOM element, tag declared in labelTagName. labelTagName should default to label if not specified when accessibleLabel is given.

• innerContent: sets the innerHTML on tagName DOM element of the Node itself.

• Reimplement useAriaLabel: {{boolean}} to setAriaLabel: {{string}} which will set the aria label attribute on the Node's DOM Element

• prependLabels: {{default false}} will be split into two options:

  • appendLabel: {{default false}}
  • appendDescription: {{ default false}}

  Notice that the default value has switched, and the default now places the label/description before the Node's DOM Element.

• parentContainerTagName exists if ever there is a label or description DOM Element, defaults to div, (implementationally defaults to null until added to the dom)

• If parentContainerTagName is given without label/description content, then just surround the single Node's tagName

• Label and description DOM Elements cannot be children to the Node's DOM element, only siblings.

• Rename parentContainerTagName -> containerTagName

[zepumph]

@jessegreenberg @mbarlow12 please add to suggest edits.

[jessegreenberg]

parentContainerTagName exists if ever there is a label or description DOM Element, defaults to div
If parentContainerTagName is given without label/description content, then just surround the single Node's tagName

These two in combination seem tricky. This means the result of specifying a parent container tag name of "div" on the node with no label or description elements will be a "no-op", which is a confusing case.

Maybe default should be null, but a div could be use if label or description elements are added and a parent container ins't specidied?

[zepumph]

agreed. I'll update the checklist above.

[zepumph]

We want to be able to disseminate the a11y api to other devs in the coming weeks, so marking as High priority.

[zepumph]

This issue is massive, so I think it may be best to work on it in pieces (perhaps breaking some pieces into separate issues). With that, to try to be as thorough as possible, I think that each piece would be good to review separately, that way we don't lose track of some nuance or forget about some pieces.

[zepumph]

#753 holds dev versions as a benchmark before diving into this issue.

[zepumph]

All that is left as part of this issue is separating out prependLabels to individual appendLabel/appendDescription. I won't have time to get to this until next week sometime.

While working in the A11y trait, I found lots of smallish things that should be fixed. For the most part, I just jotted them down, but I added a TODO also. I will create separate issues for the things I think need them.

[zepumph]

All features have been implemented with the exception of some usages of prependLabels. That will mostly happen as we go through sims in #753. Closing