fix: make line decoration link opening match Sourcegraph behavior

Prior to this change, clicking links that are provided by a Sourcegraph extension
would cause them to open in the same page. This is in contrast to what clicking
the same link on Sourcegraph does: opens in a new tab if not relative.

Fixes sourcegraph/sourcegraph-extension-api#70

Author: Stephen Gutekanst

src/libs/code_intelligence/extensions.tsx

@@ -176,6 +176,11 @@ export const applyDecoration = (
             const link = document.createElement('a')
             link.className = 'sourcegraph-extension-element'
             link.setAttribute('href', url)
+
+            // External URLs should open in a new tab, whereas relative URLs
+            // should not.
+            link.setAttribute('target', /^https?:\/\//.test(url) ? '_blank' : undefined)
+
             link.style.color = decoration.after!.color || null
             link.appendChild(e)
             return link