RFR: 8297455: Use the official ToolProvider API to call javac

[Magnus Ihse Bursie]

In JDK-8297041, the javacserver was moved out of the JDK itself, and lifted out as a separate buildtool. Due to this, internal classes in jdk.compiler were no longer available. Therefore, the closest way to calling javac as before were to use `com.sun.tools.javac.Main.compile()`. This method is however deprecated for removal, and relying on that was only needed as a temporary measure during the transition.

After the major refactoring of the javacserver tool in JDK-8297444, it will be easy to replace the Main.compile API with the official ToolProvider API instead.

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Depends on: https://git.openjdk.org/jdk/pull/11298

Commit messages:
 - 8297455: Use the official ToolProvider API to call javac

Changes: https://git.openjdk.org/jdk/pull/11299/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11299&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297455
  Stats: 10 lines in 1 file changed: 7 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11299.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11299/head:pull/11299

PR: https://git.openjdk.org/jdk/pull/11299