Reword popover "invoker" terminology to "control" or "source" where appropriate.

[keithamus]

This editorial change attempts to fix #11352, by dropping the use of the word "invoker", instead referring to the invoker as the "control". However for some algorithms "control" feels a little generic as a variable and so I opted to use "source" as it also aligns better to the IDL definitions which have a .source property to refer to said control.

IOW, a popover is controlled by a "popover control", but "source" is a specifically provided "popover control".

This also renames the "invoker command steps" and "is valid invoker command steps" to "comamndfor steps" and "is valid commandfor steps" respectively.

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/form-elements.html ( diff )
/interaction.html ( diff )
/interactive-elements.html ( diff )
/popover.html ( diff )

[domenic]

Thanks for doing this! I hadn't realized there were cases where "source" was inappropriate; could you briefly explain that for me?

[keithamus]

I think "source" works fine in instances where it refers to the IDL property. In other cases it felt a little ambiguous, for example renaming "popover invoker" to "popover source" sounds as though its the element with the popover attribute, rather than the button controlling the popover, so here I felt "popover control" was a better fit. Likewise "invoker command steps" would be odd to be named "source command steps", but also "control command steps" is equally nonsensical, so "commandfor steps" seems to be more illustrative IMO.

As an aside I don't know why CI isn't generating the preview links for this PR.