RFR: 8298971: Move Console implementation into jdk internal package

[Naoto Sato]

Moving the built-in implementation of `Console` from `java.io` package into `jdk.internal.io` package. It now implements `JdkConsole` interface and is accessed through `ProxyingConsole`.

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

Commit messages:
 - Split Console_md.c
 - 8298971: Move Console implementation into jdk internal package

Changes: https://git.openjdk.org/jdk/pull/11729/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11729&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298971
  Stats: 820 lines in 5 files changed: 425 ins; 392 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11729.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11729/head:pull/11729

PR: https://git.openjdk.org/jdk/pull/11729