RFR: 8297455: Use the official ToolProvider API to call javac [v4]

[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.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Fix merge regressions

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11299/files
  - new: https://git.openjdk.org/jdk/pull/11299/files/d2cd5690..d029b282

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11299&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11299&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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