Add ignoreList to our source maps (facebook#28310)

All our sources are considered third party and should be hidden in stack
traces unless expanded. Our internals aren't actionable anyway.

This doesn't really do much without tooling that actually forwards this
to new generated source maps, in which case they probably just add them
to ignorelist anyway.

scripts/rollup/build.js

@@ -575,6 +575,9 @@ function getPlugins(
           sourcemapAfterClosure.sources = [preMinifiedFilename];
           sourcemapAfterClosure.file = filename;
 
+          // All our code is considered "third-party" and should be ignored by default.
+          sourcemapAfterClosure.ignoreList = [0];
+
           // We'll write the pre-minified source to disk as a separate file.
           // Because it sits on disk, there's no need to have it in the `sourcesContent` array.
           // That also makes the file easier to read, and available for use by scripts.