The Java rules used toolchains of type `@bazel_tools//tools/jdk:runtime_toolchain_type` for two different purposes requiring different exec/target platform constraints, which led to issues when cross-compiling: The runtime added to the runfiles of an executable Java target has to have constraints on the target platform, whereas the runtime used to extract the bootclasspath should not have constraints on the target platform. As a result:
1. `@local_jdk` did not define any target constraints for its runtime, which allowed the runtime to provide the bootclasspath required by Android rules, but could also end up building `java_binary` targets that wouldn't run on the target (see bazelbuild#18265).
2. Remote JDKs defined a target constraint for the their runtimes, which prevented them from being added to the runfiles of targets they couldn't run on, but broke Android compilation due to the failure to resolve a runtime for bootclasspath extraction (see bazelbuild#17085).

This is resolved by adding a third toolchain type, `bootstrap_runtime_toolchain_type`, that is only used by the `bootclasspath` rule (realizes bazelbuild#17085 (comment)). Detailed explanations of the different types and their intended constraints have been added to `@bazel_tools//tools/jdk:BUILD`.

Addressing the cross-compilation errors then required the following changes:
1. Direct dependencies on the Java runtime have been removed from rules that do not need them (e.g. `android_library` and `java_binary` with `create_executable = False`).
3. Implicit dependencies on the Java runtime through the `bootclasspath` rule have been replaced with dependencies on the bootstrap runtime.
4. `{local,remote}_java_repository` now use the user-provided exec constraints of the Java toolchain as the target constraints of the associated runtime.
5. `@local_jdk` uses the auto-detected host constraints as exec constraints for the local Java toolchain.

Fixes bazelbuild#17085
Fixes bazelbuild#18265
Fixes bazelbuild/rules_java#64

RELNOTES[INC]: Java runtime toolchains created via `local_java_repository` from `@bazel_tools//tools/jdk:local_java_repository.bzl`, which includes `local_jdk`, now have `target_compatible_with` set to the auto-detected host constraints. This can result in errors about toolchain resolution failures for `@bazel_tools//tools/jdk:runtime_toolchain_type`, especially when cross-compiling. These failures can be fixed in the following ways (listed in decreasing order of preference):
* Replace `java_binary` targets that aren't meant to be run with `bazel run` or as tools during the build with `java_single_jar` (available in `@rules_java//java:java_single_jar.bzl`). Such targets do not require a Java runtime for the target configuration.
* Set `--java_runtime_version=remotejdk_N` for some Java version `N` to let Bazel choose and download an appropriate remote JDK for the current target platform. This setting defaults to `local_jdk`, which means that Bazel can only use the local JDK, which isn't compatible with any other platform.
* Manually define and register a `local_java_runtime` with no value set for `exec_compatible_with` (defaults to `[]`) and select it by setting `--java_runtime_version` to its `name`. This fully restores the previous behavior, but can result in incorrect results when cross-compiling (see bazelbuild#18265).

Closes bazelbuild#18262.

PiperOrigin-RevId: 574914446
Change-Id: I6cbfb7ffa2fbfd62e5f6fb49532b36be658dfa40

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