ColumnHider a11y issues

Ensure tab stop for column hider trigger node

Ensure tab stop for the ColumnHider trigger node and allow it to be displayed by pressing enter/space

Add keyboard nav controls

+ immediately focus first checkbox within the popup when it opens
+ allow ColumnHider popup to be dismissed by pressing escape

Add Dialog Role, Escape to close

+ Pressing Escape while the columnhider dialog is open will cauase it to close
+ focus returns to the dialog toggle button when the dialog is closed
+ Add dialog role to dialog div

Add aria-label and supporting i18n

Add aria-label to the ColumnHider popup dialog and supporting nls
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