Add fuzz test for our scanner code.

This is useful in detecting and reproducing SEGV errors,
but even after attempting to fix the issue, fuzz seems to fail in a
different way, so at this point we can't turn this on for CI.
This should create a workflow so we can manually trigger it.

Author: eed3si9n

.github/workflows/fuzz.yml

@@ -0,0 +1,25 @@
+name: Fuzz parser
+
+# Run this workflow on changes to the external scanner
+on:
+  workflow_dispatch:
+  #push:
+  #  paths:
+  #  - src/scanner.c
+  #  - src/stack.h
+  #pull_request:
+  #  paths:
+  #  - src/scanner.c
+  #  - src/stack.h
+
+jobs:
+  test:
+    name: Parser fuzzing
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: eed3si9n/tree-sitter-fuzz-action@v1
+        with:
+          language: scala
+          external-scanner: src/scanner.c
+          time: 60