RFR: 8349910: Implement HTTP/3 for the HTTP Client API

[Daniel Fuchs]

Hi,

Please find here a PR for the implementation of JEP [JDK-8291976: HTTP/3 for the HTTP Client API](https://bugs.openjdk.org/browse/JDK-8291976).

The CSR can be viewed at [JDK-8350588: Implement HTTP/3 for the HTTP Client API](https://bugs.openjdk.org/browse/JDK-8350588)

This JEP proposes to enhance the HttpClient implementation to support HTTP/3.
It adds a non-exposed / non-exported internal implementation of the QUIC protocol based on DatagramChannel and the SunJSSE SSLContext provider.

-------------

Commit messages:
 - http3: jcheck - remove trailing white spaces
 - http3: jcheck - fixed bad file permission
 - merge latest changes from master branch
 - http3: increase keepalive timeout in H3MultipleConnectionsToSameHost.java
 - http3: improve logging on reception of stateless reset
 - http3: CSR feedback: renamed H3DiscoveryMode and associated constants
 - http3: comment update in Http3PushManager.java
 - http3: more consistent connection labels; the label now includes the underlying transport-level protocol: tcp:1, tls:2, quic:1
 - Add HTTP/3 cases to `HttpResponseConnectionLabelTest`
 - http3: adapt connection label to HttpQuicConnection after merge
 - ... and 388 more: https://git.openjdk.org/jdk/compare/4eae9b5b...9c2da664

Changes: https://git.openjdk.org/jdk/pull/24751/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24751&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349910
  Stats: 102691 lines in 469 files changed: 100070 ins; 1119 del; 1502 mod
  Patch: https://git.openjdk.org/jdk/pull/24751.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24751/head:pull/24751

PR: https://git.openjdk.org/jdk/pull/24751