setup CI and tidy to use typos for spellchecking and fix few typos

.github/workflows/spellcheck.yml

@@ -0,0 +1,23 @@
+# This workflow runs spellcheck job
+
+name: Spellcheck
+on:
+  pull_request:
+    branches:
+      - "**"
+
+jobs:
+  spellcheck:
+    name: run spellchecker
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the source code
+        uses: actions/checkout@v4
+
+      - name: check typos
+        # sync version with src/tools/tidy/src/ext_tool_checks.rs in spellcheck_runner
+        uses: crate-ci/typos@v1.34.0
+        with:
+          # sync target files with src/tools/tidy/src/ext_tool_checks.rs in check_impl
+          files: ./compiler ./library ./src/bootstrap ./src/librustdoc
+          config: ./typos.toml