feat(Bootstrap): Update link color and link hover color

And move the styles from Boostrap's _reboot file to GitLab UI's
typography SCSS file.

src/scss/typography.scss

@@ -3,6 +3,19 @@ h1, h2, h3, h4, h5, h6,
   @apply gl-text-heading;
 }
 
+a {
+  @apply gl-text-link gl-no-underline hover:gl-text-link hover:gl-underline;
+}
+
+// Copied from https://gitlab.com/gitlab-org/gitlab-ui/-/blob/5db1e111501c9e252a388a780e2789dce11dedf4/src/vendor/bootstrap/scss/_reboot.scss#L194.
+// And undo these styles for placeholder links/named anchors (without href).
+// It would be more straightforward to just use a[href] in previous block, but that
+// causes specificity issues in many other styles that are too complex to fix.
+// See https://github.com/twbs/bootstrap/issues/19402
+a:not([href]):not([class]) {
+  @apply gl-text-inherit gl-no-underline hover:gl-text-inherit hover:gl-no-underline;
+}
+
 caption {
   @apply gl-text-subtle;
-}
\ No newline at end of file
+}

src/vendor/bootstrap/scss/_reboot.scss

@@ -176,37 +176,6 @@ sub { bottom: -.25em; }
 sup { top: -.5em; }
 
 
-//
-// Links
-//
-
-a {
-  color: $link-color;
-  text-decoration: $link-decoration;
-  background-color: transparent; // Remove the gray background on active links in IE 10.
-
-  @include hover() {
-    color: $link-hover-color;
-    text-decoration: $link-hover-decoration;
-  }
-}
-
-// And undo these styles for placeholder links/named anchors (without href).
-// It would be more straightforward to just use a[href] in previous block, but that
-// causes specificity issues in many other styles that are too complex to fix.
-// See https://github.com/twbs/bootstrap/issues/19402
-
-a:not([href]):not([class]) {
-  color: inherit;
-  text-decoration: none;
-
-  @include hover() {
-    color: inherit;
-    text-decoration: none;
-  }
-}
-
-
 //
 // Code
 //