fix(OverflowMenu): remove default tabindex and SVG focusable attribute

[emyarod]

Closes #6935

This PR removes the redundant default tabindex value on the overflow menu trigger button and also removes the redundant focusable attribute from the icon props. It looks like the focusable="false" was meant to prevent extra tab stops in IE11, but I was unable to replicate that issue

Changelog

Removed

• default tabindex value
• focusable attribute on trigger button SVG

Testing / Reviewing

Confirm that the trigger button no longer receives a tabindex value by default and that there are no changes to focus behavior and tab stops particularly in IE11

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[dakahn]

Seems like this has broken keyboard controls for the menu itself on Firefox latest

[emyarod]

that was a separate existing issue fixed in #6978, try updating your branch to pull in the latest commits to Carbon

[joshblack]

bump @dakahn @tw15egan when you get a sec today 👀

[tw15egan]

LGTM 👍 ✅

[carmacleod]

For the record, it was not the focusable=false on the SVG that was unnecessary, it was the focusable="false" on the span inside the SVG. A google of "SVG focusable=false IE11" still finds a lot of hits, so you may still need focusable=false on the SVG itself. (Note that the bug was fixed in old Edge, but as far as I know it was never fixed in IE11, so I'm surprised that you didn't see an extra tab stop in IE11)

[emyarod]

yeah the SVG itself still has focusable=false by default since that attribute is added when we generate our icons

[carmacleod]

Ah, ok. Thanks for the explanation. I was confused by the title and opening comment in this PR. :)
I just tested whether SVGs in IE11 still need the focusable=false, and they definitely still need it.
Here's my little test case: https://carmacleod.github.io/playground/svg-test.html
(Just FYI at this point, since you didn't actually delete the focusable=false from the SVG itself 😄 )