android_library doesn't work with the Java 11 language level

[cushon]

cc @ahumesky

Trying to use the Java 11 language level (--java_language_level=11) with android_library doesn't work.

Starting in Java 9, javac requires the --system flag to be set instead of the --bootclasspath to configure the system APIs. That includes APIs like java.lang.*, and also things like android.* for Android compilations.

The shared logic for Java compilations supports this using the BootClassPathInfo provider, which can represent the arguments to javac's --system flag. But this isn't wired up for android_library, which just configures a legacy --bootclasspath that gets ignored, resulting in errors like package android.app does not exist.

Repro

git diff HEAD
diff --git a/android/tutorial/WORKSPACE b/android/tutorial/WORKSPACE
new file mode 100644
index 0000000..9cc43bb
--- /dev/null
+++ b/android/tutorial/WORKSPACE
@@ -0,0 +1 @@
+android_sdk_repository(name = "androidsdk")
diff --git a/android/tutorial/src/main/java/com/example/bazel/BUILD b/android/tutorial/src/main/java/com/example/bazel/BUILD
new file mode 100644
index 0000000..76f8ba7
--- /dev/null
+++ b/android/tutorial/src/main/java/com/example/bazel/BUILD
@@ -0,0 +1,13 @@
+package(
+    default_visibility = ["//src:__subpackages__"],
+)
+
+android_library(
+    name = "greeter_activity",
+    srcs = [
+        "Greeter.java",
+        "MainActivity.java",
+    ],
+    manifest = "AndroidManifest.xml",
+    resource_files = glob(["res/**"]),
+)

With bazel built at 78c5e417ec981609687594eb70d8569aaa9e7f1c

$ bazel build --java_language_version=11 ...
INFO: Analyzed target //src/main/java/com/example/bazel:greeter_activity (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
ERROR: /tmp/tmp.EBbQNtnZOD/examples/android/tutorial/src/main/java/com/example/bazel/BUILD:5:16: Building src/main/java/com/example/bazel/libgreeter_activity.jar (2 source files) failed: (Exit 1): java failed: error executing command (from target //src/main/java/com/example/bazel:greeter_activity) external/remotejdk17_linux/bin/java '--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED' '--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED' ... (remaining 17 arguments skipped)
warning: [options] system modules path not set in conjunction with -source 11
src/main/java/com/example/bazel/MainActivity.java:3: error: package android.app does not exist
import android.app.Activity;
                  ^

[cushon]

[see also b/237102742]

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