Replace angle icons with chevron

In gitlab-design#704 (closed) the process of consolidating icon terms started, and this is a progression of it where angles will be deprecated in favor of chevrons. After the remapping is complete in the product, then the SVGs can be removed from the SVG library.

Icon	Current name	New name
	angle-double-left	chevron-double-lg-left
	angle-double-right	chevron-double-lg-right
	angle-down	chevron-lg-down
	angle-left	chevron-lg-left
	angle-right	chevron-lg-right
	angle-up	chevron-lg-up

Checklist

• chevron-double-lg-left
• chevron-double-lg-right
• chevron-lg-down
• chevron-lg-left
• chevron-lg-right
• chevron-lg-up

This issue will be closed when all related MRs are validated in prod.