RFR: 8344233: Remove calls to SecurityManager and doPrivileged in java.net.ProxySelector and sun.net.spi.DefaultProxySelector after JEP 486 integration

[Jaikiran Pai]

Can I please get a review of this change which removes calls to `SecurityManager` and `AccessController.doPrivileged()` from the `ProxySelector` and `DefaultProxySelector` classes?

Apart from the trivial removing of those calls, the commit in this PR also removes the `getProxySelector` and `setProxySelector` named `NetPermission`s. These 2 named permissions, were previously only documented on the `ProxySelector.getDefault()` and `ProxySelector.setDefault()` methods. With the removal of SecurityManager, the specification of these named properties ceases to exist. Having said that, would removal of these named NetPermission(s) require a CSR linked to this current issue?

The other major chunk of this change is moving the proxy determination logic in `DefaultProxySelector` into a private method from the previous `doPriveleged()` call block.

No new tests have been introduced. Existing tests in tier1 and tier2 continue to pass with this change.

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Commit messages:
 - 8344233: Remove calls to SecurityManager and doPrivileged in java.net.ProxySelector and sun.net.spi.DefaultProxySelector after JEP 486 integration

Changes: https://git.openjdk.org/jdk/pull/22145/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22145&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344233
  Stats: 234 lines in 4 files changed: 74 ins; 123 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/22145.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22145/head:pull/22145

PR: https://git.openjdk.org/jdk/pull/22145