Refactor snapshot build (#2825)

Instead of using core/snapshot_creator.rs, instead two crates are
introduced which allow building the snapshot during build.rs.

Rollup is removed and replaced with our own bundler. This removes
the Node build dependency. Modules in //js now use Deno-style imports
with file extensions, rather than Node style extensionless imports.

This improves incremental build time when changes are made to //js files
by about 40 seconds.

js/dispatch_json_test.ts

@@ -2,9 +2,9 @@ import { testPerm, assertMatch, unreachable } from "./test_util.ts";
 
 const openErrorStackPattern = new RegExp(
   `^.*
-    at unwrapResponse \\(js\\/dispatch_json\\.ts:.*\\)
-    at sendAsync.* \\(js\\/dispatch_json\\.ts:.*\\)
-    at async Object\\.open \\(js\\/files\\.ts:.*\\).*$`,
+    at unwrapResponse \\(.*dispatch_json\\.ts:.*\\)
+    at Object.sendAsync \\(.*dispatch_json\\.ts:.*\\)
+    at async Object\\.open \\(.*files\\.ts:.*\\).*$`,
   "ms"
 );