Use compilations instead of multiple mpp targets for java codegen tests

[martinbonnin]

Inspired from https://youtrack.jetbrains.com/issue/KT-61007

This introduces an intermediate kotlinCodegenTest source set that is common to everything except javaCodegen. Our sourceSet graph for tests is now like this:

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[BoD]

Neat! 🎉

[martinbonnin]

Build scans

• Before
  • apollo-kotlin https://ge.apollographql.com/s/ezzplv3ttifbw
  • apollo-tests https://ge.apollographql.com/s/oat2hvd4xf2ge
• After
  • apollo-kotlin https://ge.apollographql.com/s/iyaarjqicguka
  • apollo-tests https://ge.apollographql.com/s/5npnxfyyupr74

There were more native tasks executed here, will dig into it

[martinbonnin]

We used to add targets for both macosArm64 and macosX64 while tests were running only on one of those (but compilation can be run for both). By only adding the host target, we should save a bit of time.

[martinbonnin]

1131 tests executed

macosX64 tests are executed here

Merging this.