[m-rev.] for review: implement the rest of the extension changes proposal

[Julien Fischer]

On Fri, 18 Aug 2023, Julien Fischer wrote:

>
> On Thu, 17 Aug 2023, Zoltan Somogyi wrote:
>
>>  For review by anyone, and for tryout by Julien on Windows.
>
> This evening's ROTD build has fallen over while attempting to install
> the Java grade; I suspect it is this change.
>
> The error is below, but th relevant information is probably the
> command line used to invoke the Java compiler, which isn't captured
> in the .err file.

At a guess, the issue is likely that compiler/compile_target_code.m
still has references to the classs directories (which are now named
classes.)

Julien.