Add a comment to run source map symbolication on the main thread for debugging

It proved somewhat difficult when I had the debug the source map
symbolication worker on the worker thread. It makes things a lot easier
when it runs on the main thread instead. I tried adding a const flag for
this with its proper function, but esbuild wasn't properly removing the
dead code, so it was inflating the bundle a lot when this function was
there even if it was unused.

I tried also converting that into an async import, which extracted the
symbolication into a different bundle, but it was still outputting the
extra bundle even if it was false constant value. So, I decided to
include it as a commented out documentation in case we need it in the
future. It's not the best, but it should still help us when we need to
debug the worker in the future.

Author: canova

src/actions/source-map-symbolication.ts

@@ -76,6 +76,29 @@ export function doSourceMapSymbolication(
  * Spawn a one-shot source map worker, send it the input, and return the
  * output. The worker is terminated once a response is received or an error
  * occurs. Uses the same on-demand spawn pattern as gz.browser.ts.
+ *
+ * Debugging tip: to step through symbolication from the page DevTools, paste
+ * the snippet below over this function body. It runs the same core on the
+ * main thread (blocking, debug only).
+ *
+ *   const { runSourceMapSymbolicationCore } = await import(
+ *     'firefox-profiler/profile-logic/source-map-symbolication'
+ *   );
+ *   const sources = {
+ *     length: input.sources.length,
+ *     id: input.sources.id.slice(),
+ *     filename: input.sources.filename.slice(),
+ *     startLine: input.sources.startLine.slice(),
+ *     startColumn: input.sources.startColumn.slice(),
+ *     sourceMapURL: input.sources.sourceMapURL.slice(),
+ *     content: input.sources.content.slice(),
+ *   };
+ *   const stringArray = input.stringArray.slice();
+ *   const wasmUrl = new URL('/mappings.wasm', window.location.href).href;
+ *   return runSourceMapSymbolicationCore(
+ *     { ...input, sources, stringArray },
+ *     wasmUrl
+ *   );
  */
 function _runSourceMapWorker(input: WorkerInput): Promise<WorkerOutput> {
   return new Promise((resolve) => {