doc: restore documentation for two error codes

[ChALkeR]

ERR_HTTP2_ERROR and ERR_UNKNOWN_BUILTIN_MODULE error codes documentation seem to have been accidentally removed in commit 1cdb41f (pull request #15160).

This reverts that removal, restoring the documentation for those two error codes.

Those error codes are used from lib/ folder.

This is a part of the fixes hinted by #21470, which includes some tests
for error codes usage and documentation and enforces a stricter format.

I split this into a separate commit/PR as this should be easy to land (and backport if needed), and some of the other fixes are more heavy and/or controversial.

Refs: #21470, #21440, #15160

Tests are not included — #21470 does that.

Exact usage locations:

node/lib/internal/bootstrap/loaders.js

Lines 146 to 150 in a40e062

	// eslint-disable-next-line no-restricted-syntax
	const err = new Error(`No such built-in module: ${id}`);
	err.code = 'ERR_UNKNOWN_BUILTIN_MODULE';
	err.name = 'Error [ERR_UNKNOWN_BUILTIN_MODULE]';
	throw err;

node/lib/internal/http2/util.js

Lines 471 to 478 in a40e062

	class NghttpError extends Error {
	constructor(ret) {
	super(binding.nghttp2ErrorString(ret));
	this.code = 'ERR_HTTP2_ERROR';
	this.name = 'Error [ERR_HTTP2_ERROR]';
	this.errno = ret;
	}
	}

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[nodejs-github-bot]

@ChALkeR build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/131/pipeline

[ChALkeR]

/cc @gnbezerra, @BridgeAR, @jasnell

[ChALkeR]

Note: I consider this as a partial revert and specifically do not want to change the documentation of those error codes in the process of restoring it — that should be done separately, if needed.

[ChALkeR]

8.x, 9.x, 10.x are affected, 6.x is not affected.

[ChALkeR]

👍 on this comment for fast-track (sorry for not mentioning it earlier).

[ChALkeR]

Landed in cdb5985, thanks!