RFR: 8344223: Remove calls to SecurityManager and doPrivileged in java.net.URLClassLoader after JEP 486 integration

[Jaikiran Pai]

Can I please get a review of this change which proposes to remove SecurityManager related API usages from `URLClassLoader` and its related `URLClassPath`? This addresses https://bugs.openjdk.org/browse/JDK-8344223.

The `URLClassLoader.getPermissions()` method will need additional changes but that will be done as part of https://bugs.openjdk.org/browse/JDK-8343150.

I'll be opening a CSR for this change because we are removing support for the `jdk.net.URLClassPath.disableRestrictedPermissions` system property.

No new tests have been added and existing tier1, tier2 and tier3 tests continue to pass.

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Commit messages:
 - 8344223: Remove calls to SecurityManager and doPrivileged in java.net.URLClassLoader after JEP 486 integration

Changes: https://git.openjdk.org/jdk/pull/22233/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22233&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344223
  Stats: 423 lines in 3 files changed: 26 ins; 311 del; 86 mod
  Patch: https://git.openjdk.org/jdk/pull/22233.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22233/head:pull/22233

PR: https://git.openjdk.org/jdk/pull/22233