esm: unflag Module.register and allow nested loader import()

Major functional changes:

- Allow `import()` to work within loaders that require other loaders,
- Unflag the use of `Module.register`.

A new interface `Customizations` has been created in order to unify
`ModuleLoader` (previously `DefaultModuleLoader`), `Hooks` and
`CustomizedModuleLoader` all of which now implement it:

```ts
interface LoadResult {
  format: ModuleFormat;
  source: ModuleSource;
}

interface ResolveResult {
  format: string;
  url: URL['href'];
}

interface Customizations {
  allowImportMetaResolve: boolean;
  load(url: string, context: object): Promise<LoadResult>
  resolve(
    originalSpecifier:
    string, parentURL: string,
    importAssertions: Record<string, string>
  ): Promise<ResolveResult>
  resolveSync(
    originalSpecifier:
    string, parentURL: string,
    importAssertions: Record<string, string>
  ) ResolveResult;
  register(specifier: string, parentUrl: string): any;
  forceLoadHooks(): void;
  importMetaInitialize(meta, context, loader): void;
}
```

The `ModuleLoader` class now has `setCustomizations` which takes an
object of this shape and delegates its responsibilities to this object
if present.

Note that two properties `allowImportMetaResolve` and `resolveSync`
exist now as a mechanism for `import.meta.resolve` – since `Hooks`
does not implement `resolveSync` other loaders cannot use
`import.meta.resolve`; `allowImportMetaResolve` is a way of checking
for that case instead of invoking `resolveSync` and erroring.

Fixes https://github.com/nodejs/node/issues/48515
Closes https://github.com/nodejs/node/pull/48439

PR-URL: https://github.com/nodejs/node/pull/48559
Reviewed-By: Jacob Smith <jacob@frende.me>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>

doc/api/errors.md

@@ -1233,23 +1233,6 @@ provided.
 Encoding provided to `TextDecoder()` API was not one of the
 [WHATWG Supported Encodings][].
 
-<a id="ERR_ESM_LOADER_REGISTRATION_UNAVAILABLE"></a>
-
-### `ERR_ESM_LOADER_REGISTRATION_UNAVAILABLE`
-
-<!-- YAML
-added: REPLACEME
--->
-
-Programmatically registering custom ESM loaders
-currently requires at least one custom loader to have been
-registered via the `--experimental-loader` flag. A no-op
-loader registered via CLI is sufficient
-(for example: `--experimental-loader data:text/javascript,`;
-do not omit the necessary trailing comma).
-A future version of Node.js will support the programmatic
-registration of loaders without needing to also use the flag.
-
 <a id="ERR_EVAL_ESM_CANNOT_PRINT"></a>
 
 ### `ERR_EVAL_ESM_CANNOT_PRINT`