feat(breadcrumb): Set default separator and fix spacing

What does this MR do?

Couple of breadcrumb UI improvements - Closes #1580 (closed), #1582 (closed), #1584 (closed), and #1585 (closed)

Fix markup of li elements
Move avatar and separator inside breadcrumb item
Reduce spacing around separator
Absolute positioning so separator isn't included in focus styles

before	after

Using absolute positioning so when focused it looks like this:

instead of this:

Does this MR meet the acceptance criteria?

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Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

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