RFR: 8344420: Remove Security Manager dependencies from javax.security package [v2]

[Sean Mullan]

> Now that JEP 486 has been integrated, the `javax.security` package implementation dependencies on `System.getSecurityManager`, `AccessController.doPrivileged` and `AccessControlContext` can be removed.
> 
> Most of the changes are straightforward: removal of code calling `System.getSecurityManager()` and unwrapping of code inside `AccessController.doPrivileged`. However, two changes involved slightly more complicated work:
> 
> 1. `javax.security.auth.login.Configuration` and `javax.security.auth.login.LoginContext` do not need to capture the caller's access control context anymore.
> 2. The `SecureSet` implementation in `javax.security.auth.Subject` is greatly simplified because it does not do security checks anymore.

Sean Mullan has updated the pull request incrementally with one additional commit since the last revision:

  Restore some local variables to be final.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22368/files
  - new: https://git.openjdk.org/jdk/pull/22368/files/c3e2a5ed..66c930e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22368&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22368&range=00-01

  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/22368.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22368/head:pull/22368

PR: https://git.openjdk.org/jdk/pull/22368