refactor(core): remove ext: modules from the module map (#19040)

Rather than disallowing `ext:` resolution, clear the module map after
initializing extensions so extension modules are anonymized. This
operation is explicitly called in `deno_runtime`. Re-inject `node:`
specifiers into the module map after doing this.

Fixes #17717.

cli/build.rs

@@ -40,7 +40,7 @@ mod ts {
 
     let node_built_in_module_names = SUPPORTED_BUILTIN_NODE_MODULES
       .iter()
-      .map(|s| s.name)
+      .map(|p| p.module_name())
       .collect::<Vec<&str>>();
     let build_libs = state.borrow::<Vec<&str>>();
     json!({