RFR: JDK-8261510: Use RFC numbers rather than protocol or draft names in sun.security.ssl.SSLExtension

[John Jiang]

This is a simple cleanup for sun.security.ssl.SSLExtension.
It converts protocol or draft names to RFC numbers correspondingly.
It also removes a trailing space in extension token_binding, and move signature_algorithms_cert to RFC 8446 extension group.

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Commit messages:
 - JDK-8261510

Changes: https://git.openjdk.java.net/jdk/pull/2517/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2517&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261510
  Stats: 46 lines in 1 file changed: 19 ins; 22 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2517.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2517/head:pull/2517

PR: https://git.openjdk.java.net/jdk/pull/2517