RFR: 8282515: More clean up on NativeLibraries just for JNI library use [v2]

[Mandy Chung]

> This patch further cleans up NativeLibraries just for JNI library use.  RawNativeLibraries implements its own native load and unload methods.  In addition, this also fixes the implementation of `RawNativeLibraries::load` not to throw UnsatisfiedLinkError if a library cannot be loaded for any reason but instead returns null.

Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:

  fix no newline at end of file

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7661/files
  - new: https://git.openjdk.java.net/jdk/pull/7661/files/eae60a40..cbdc39ed

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7661&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7661&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7661.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7661/head:pull/7661

PR: https://git.openjdk.java.net/jdk/pull/7661