Adds a script for removing unused diagnostics (#44324)

* Adds a script for removing unused diagnostics

* Accidentally deleted the wrong one

scripts/find-unused-diganostic-messages.mjs

@@ -0,0 +1,30 @@
+// @ts-check
+// This file requires a modern version of node 14+, and grep to be available.
+
+// node scripts/find-unused-diagnostic-messages.mjs
+import { readFileSync } from "fs";
+import {EOL} from "os";
+import { execSync } from "child_process";
+
+const diags = readFileSync("src/compiler/diagnosticInformationMap.generated.ts", "utf8");
+const startOfDiags = diags.split("export const Diagnostics")[1];
+
+const missingNames = [];
+startOfDiags.split(EOL).forEach(line => {
+    if (!line.includes(":")) return;
+    const diagName = line.split(":")[0].trim();
+
+    try {
+        execSync(`grep -rnw 'src' -e 'Diagnostics.${diagName}'`).toString();
+        process.stdout.write(".");
+    } catch (error) {
+        missingNames.push(diagName);
+        process.stdout.write("x");
+    }
+});
+
+if (missingNames.length) {
+    process.exitCode = 1;
+    console.log("Could not find usage of these diagnostics in the codebase:");
+    console.log(missingNames);
+}