Bloop doesn't "unload" compiler plugins

[alexarchambault]

When enabling Scala.JS or Scala Native, it seems bloop doesn't disable them if we don't enable them later on:

$ rm -rf examples/utest/.scala utest-j*.jar

$ /mill -i cli.run package examples/utest --library -o utest-jvm.jar
$ unzip -l utest-jvm.jar
Archive:  utest-jvm.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
       25  06-10-2021 16:51   META-INF/MANIFEST.MF
     1338  06-10-2021 16:51   MyTests.class
     3912  06-10-2021 16:51   MyTests$.class
---------                     -------
     5275                     3 files

$ ./mill -i cli.run package examples/utest --library -o utest-js.jar --js
$ unzip -l utest-js.jar
Archive:  utest-js.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
       25  06-10-2021 16:58   META-INF/MANIFEST.MF
     1338  06-10-2021 16:58   MyTests.class
     1067  06-10-2021 16:58   MyTests.sjsir
     3441  06-10-2021 16:58   MyTests$.sjsir
     3912  06-10-2021 16:58   MyTests$.class
---------                     -------
     9783                     5 files

$ ./mill -i cli.run package examples/utest -o utest-native.jar --native --library
$ unzip -l utest-native.jar
Archive:  utest-native.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
       25  06-10-2021 16:59   META-INF/MANIFEST.MF
     1338  06-10-2021 16:59   MyTests.class
     1067  06-10-2021 16:58   MyTests.sjsir
     3441  06-10-2021 16:58   MyTests$.sjsir
     3912  06-10-2021 16:59   MyTests$.class
    15987  06-10-2021 16:59   MyTests$.nir
     1596  06-10-2021 16:59   MyTests$$$Lambda$4.nir
     1599  06-10-2021 16:59   MyTests$$$Lambda$5.nir
     1906  06-10-2021 16:59   MyTests$$$Lambda$1.nir
     1906  06-10-2021 16:59   MyTests$$$Lambda$2.nir
     1182  06-10-2021 16:59   MyTests$$SN$ReflectivelyInstantiate$.nir
     1596  06-10-2021 16:59   MyTests$$$Lambda$3.nir
---------                     -------
    35555                     12 files

$ ./mill -i cli.run package examples/utest --library -o utest-jvm-after-js-and-native.jar
$ unzip -l utest-jvm-after-js-and-native.jar
Archive:  utest-jvm-after-js-and-native.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
       25  06-10-2021 17:01   META-INF/MANIFEST.MF
     1338  06-10-2021 17:01   MyTests.class
     1067  06-10-2021 16:58   MyTests.sjsir
     3441  06-10-2021 16:58   MyTests$.sjsir
     3912  06-10-2021 17:01   MyTests$.class
    15987  06-10-2021 16:59   MyTests$.nir
     1596  06-10-2021 16:59   MyTests$$$Lambda$4.nir
     1599  06-10-2021 16:59   MyTests$$$Lambda$5.nir
     1906  06-10-2021 16:59   MyTests$$$Lambda$1.nir
     1906  06-10-2021 16:59   MyTests$$$Lambda$2.nir
     1182  06-10-2021 16:59   MyTests$$SN$ReflectivelyInstantiate$.nir
     1596  06-10-2021 16:59   MyTests$$$Lambda$3.nir
---------                     -------
    35555                     12 files

That's in spite of scala clearing the class output directory before each run. (bloop seems to copy the .sjsir and .nir files from its internal class directory).