Meta: Disambiguate focus() and blur() for Window and HTMLElement

[zcorpan]

Add data-for="" attributes as appropriate. This should help other
specs (in this case CSSOM View) cross-referencing these terms.

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cc @tabatkins

The link error in cssom-view I'm trying to fix here is:

LINK ERROR: Multiple possible 'focus()' idl refs for 'HTMLElement'.
Arbitrarily chose https://html.spec.whatwg.org/multipage/interaction.html#dom-focus
The following refs show up multiple times in their spec, in a way that Bikeshed can't distinguish between. Either create a manual link, or ask the spec maintainer to add disambiguating attributes (usually a for='' attribute to all of them).
spec:html; type:method; for:HTMLElement; text:focus()
  https://html.spec.whatwg.org/multipage/interaction.html#dom-focus
  https://html.spec.whatwg.org/multipage/interaction.html#dom-window-focus
<a data-link-type="idl" data-lt="focus()" data-link-for="HTMLElement">focus()</a>
 ✔  Successfully generated, with 1 linking errors

[domenic]

Isn't it data-dfn-for?

[zcorpan]

https://tabatkins.github.io/bikeshed/#dfn-contract ... yes. Will fix. There were some more data-fors also.

[tabatkins]

👍 after fixing the attribute name