PageHeader: Address dom order issues (screen reader experience feedback from sign-off) (#4358)

* Update layout styles so that all interactive elements come after the title

* Add PageHeder.Breadcrumbs sub component

* remove shapshot check on jest

* test(vrt): update snapshots

* test(vrt): update snapshots

* make the interactive element in the heading check a warning not error

* add pageheader story for screen reader tes

* add links

* add onclick events to the buttons

* add a placeholder for file content example

* test(vrt): update snapshots

* elements losing context when viewport is narrrow - keep the same text for buttons in all viewports

* fix linting

* test(vrt): update snapshots

* hide the overflow menu in narrow since we show it on the context area

* accomodate different format sx prop for font size

* when no fontsize is specified css var returns as an empty string so need ternary instead of Nullish coalescing

* temporary fix on navlist

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Co-authored-by: broccolinisoup <[email protected]>

Author: broccolinisoup