Add mechanism for different package managers to contribute their installed JVM toolchains

[big-guy]

Instead of embedding multiple implementations for each type of package manager (ASDF, SDKMAN!, etc) into Gradle itself, like repositories, users should be able to configure their build to look in different locations (or providers) for installed JVM toolchains.

As part of this, we would introduce a mechanism for users to configure this, deprecate the built-in mechanisms and eventually remove them.

[dkowis]

Good plan! Looking forward to being able to contribute something to do this :D

[kravemir]

Ideally, convention over configuration, something that gradle (wrapper) could automatically pick up from environment, without a need to modify anything in gradle files, i.e. not having to adjust gradle.properties to set org.gradle.java.installations.fromEnv=JDK8,JRE17.

Something like Linux's PATH environment variable would be nice to have - comma delimited paths. Maybe JAVA_HOMES, JAVA_PATH(S), GRADLE_JAVA_HOMES, GRADLE_JAVA_PATH(S) or else.

Regarding #29214 attempt for Nix. Per-directory setup can be achieved with tool like direnv with use nix, that would just set gradle's default env variable, and wrapper should work okay. For NixOS (#29214), the env var can be set globally.