RFR: 8271627: Use local field access in favor of Class.getClassLoader0

[Claes Redestad]

Trivial startup hack/cleanup to use the `classLoader` field directly rather than the `getClassLoader0` accessor. 

Before aa12c8fbf5b020d168cf29412643bf15514b0439 there was no `classLoader` field and `getClassLoader0` was a native method that retrieved the `ClassLoader` by calling into the runtime. However, now that `classLoader` is injected on mirror creation it makes less sense to use the accessor when not necessary.

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

Commit messages:
 - Merge branch 'master' into startup_classLoader0
 - Avoid getClassLoader0 calls from within Class
 - Reuse SecurityConstants.ACCESS_PERMISSION from MethodHandles

Changes: https://git.openjdk.java.net/jdk/pull/4960/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4960&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271627
  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4960.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4960/head:pull/4960

PR: https://git.openjdk.java.net/jdk/pull/4960