RFR: 8295803: Console should be usable in jshell and other environments

[Naoto Sato]

This is to allow Console to be used even when it is not attached to the platform provided terminal, such as the case when the standard input is redirected. `System.console()` now returns a Console implementation based on `jdk.internal.le` terminal by default, or jshell implementation if available. A corresponding CSR has been drafted.

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Commit messages:
 - Minor fixup
 - GetPropertyAction.privilegedGetProperty
 - Changed to use SharedSecrets
 - Password.readPassword() fix
 - Always returns Console, even without TTY attached
 - Comments refresh, clean-up
 - Removed charset from factory, added new jdk.console property
 - Revived the provider i/f
 - Replacing SPI with proxy delegate
 - javadoc
 - ... and 3 more: https://git.openjdk.org/jdk/compare/ae5b1f76...96a46843

Changes: https://git.openjdk.org/jdk/pull/11421/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11421&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295803
  Stats: 387 lines in 10 files changed: 373 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/11421.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11421/head:pull/11421

PR: https://git.openjdk.org/jdk/pull/11421