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

[Magnus Ihse Bursie]

On Tue, 22 Nov 2022 20:50:04 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> 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.

Well, I assume so. If this does not work properly, the problem will most likely be already in JDK-8297444; this patch is just choosing a different path to end up in the same class, as far as I can understand.

The thing that makes (or should make) us chose the interim javac is the `$(INTERIM_LANGTOOLS_ARGS)` which is passed to java when launching the server. (This is since these flags are passed in the config file to the client as `javacmd`). 

I'll add some test output code to the interim compiler to verify that it is actually executed, both in JDK-8297444 and in this PR.

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