TLS module: Support multiple ecdhCurve's

[Hativ]

The tls module respectively tls.createSecureContext should support multiple echdCurve's like nginx does.

Example:

const options = {
   ecdhCurves: 'x25519:secp521r1:secp384r1',
 };

The order should be honored (perhaps configurable like honorChiperOrder).

[bnoordhuis]

Pull requests welcome. The way to do it is to call SSL_CTX_set_ecdh_auto() + SSL_CTX_set1_curves() or SSL_CTX_set1_curves_list(). We currently call SSL_CTX_set_tmp_ecdh(), that may have to change.

An array of strings is arguably a little more idiomatic in node.js but it's probably not a deal breaker.

honorChiperOrder should already affect who gets to select the curve, client or server.

[bnoordhuis]

Closing, #15206 was merged and is scheduled to be released in v8.6.0.