[Links] Show external-link icon where applicable

[meissadia]

Close #765

Note: May result in unwanted wrapping of icon. Example below (the regulation link):

Changes

• Adds the external-link icon automatically when we determine it's a non-cfgov link
• Overrides DS Notification styles to ensure icon colors consistently match link status-based (visited, hover) styles

[meissadia]

@natalia-fitzgerald Please follow-up with devs on how we want to handle external links where the icon wraps to a new line.

One potential solution is to use the Link component's noWrap property, which would keep the link text + icon together, but looks like it could introduce it's own wrapping oddities. Example screenshot below:

Description	Screenshot
Without noWrap (allow link text to wrap)
With noWrap (prevent link text from wrapping)

[natalia-fitzgerald]

@meissadia
Can you show the same two screenshots at mobile? I do worry that forcing no wrap could introduce even further oddities at smaller screen widths.

[meissadia]

@meissadia Can you show the same two screenshots at mobile? I do worry that forcing no wrap could introduce even further oddities at smaller screen widths.

@natalia-fitzgerald On large mobile (width: 425px)

Regular	No wrap

[natalia-fitzgerald]

@meissadia
Would it be possible to push the no wrap solution to a dev server so that I can click around and see how that approach looks across a few instances?