client/web: button, link, and other small UI updates

Makes the following changes:
* Use “link” class in various spots
* Remove button appearance on Exit Node dropdown in readonly mode
* Update `-stone-` colors to `-gray-` (couple spots missed by
  original color config commit)
* Pull full ui/button component from admin panel, and update
  buttons throughout UI to use this component
* Remove various buttons in readonly view to match mocks
* Add route (and “pending approval”) highlights to Subnet router
  settings card
* Delete legacy client button styles from index.css
* Fix overflow of IPv6 address on device details view

Updates #10261

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

client/web/src/ui/loading-dots.tsx

@@ -0,0 +1,23 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+import cx from "classnames"
+import React, { HTMLAttributes } from "react"
+
+type Props = HTMLAttributes<HTMLDivElement>
+
+/**
+ * LoadingDots provides a set of horizontal dots to indicate a loading state.
+ * These dots are helpful in horizontal contexts (like buttons) where a spinner
+ * doesn't fit as well.
+ */
+export default function LoadingDots(props: Props) {
+  const { className, ...rest } = props
+  return (
+    <div className={cx(className, "loading-dots")} {...rest}>
+      <span />
+      <span />
+      <span />
+    </div>
+  )
+}