chore(repo): Deprecate node@{14,15,16,17} versions (#1864)

* feat(shared): Introduce isomorphicBtoa helper

* chore(repo): Upgrade to node@18 + moved dev dependencies

* chore(repo): Update READMEs with node@18 prerequisite

* chore(backend): Drop fetch and crypto polyfills

* chore(*): Make engines, @types/node and README refs to include node patch version

* chore(*): Add changeset

Author: dimkl

.changeset/little-numbers-jam.md

@@ -0,0 +1,5 @@
+---
+'@clerk/shared': minor
+---
+
+Introduce isomorphic `isomorphicBtoa` helper in `@clerk/shared`.

.changeset/purple-pumas-study.md

@@ -0,0 +1,16 @@
+---
+'gatsby-plugin-clerk': major
+'@clerk/chrome-extension': major
+'@clerk/clerk-js': major
+'@clerk/clerk-sdk-node': major
+'@clerk/backend': major
+'@clerk/fastify': major
+'@clerk/nextjs': major
+'@clerk/shared': major
+'@clerk/themes': major
+'@clerk/clerk-react': major
+'@clerk/remix': major
+'@clerk/types': major
+'@clerk/clerk-expo': major
+---
+Dropping support for Node 14 and 16 as they both reached EOL status. The minimal Node.js version required by Clerk is `18.18.0` now.