Revise management of Eclipse-related Java versions (#1866)

The `com.ibm.wala.jdk-version` Gradle property determines the Java
toolchain used for compiling and testing Java code. Previously, it also
influenced the Java release used when compiling Eclipse-_dependent_ Java
code. However, this property does _not_ influence the Java release used
when compiling Elipse-_independent_ code. Rather, [the latter is always
hard-coded to release
11](https://github.com/wala/WALA/blob/c9fdc915544051266700e0cacaea0e0ab7bd5877/build-logic/src/main/kotlin/com/ibm/wala/gradle/java.gradle.kts#L62).

Now we hard-code the Java release used when compiling Eclipse-dependent
code too: 17, not 11, because some Eclipse dependencies use 17.

When using the ECJ batch compiler, set the Java release using `--release
N` instead of `-source N -target N` or simply `-N`. [The documentation
on how these flags interact is
poor](https://help.eclipse.org/latest/index.jsp?topic=%2Forg.eclipse.jdt.doc.user%2Ftasks%2Ftask-using_batch_compiler.htm).
But after experimenting and examining [the ECJ
implementation](https://github.com/eclipse-jdt/eclipse.jdt.core/blob/5da60278fd97d15570cbbc07219a6ab525d91feb/org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/batch/Main.java),
I believe that `--release N` does everything that `-N -source N -target
N` would do.

Author: liblit

build-logic/src/main/kotlin/com/ibm/wala/gradle/JavaCompileUsingEcj.kt

@@ -52,10 +52,8 @@ abstract class JavaCompileUsingEcj : JavaCompile() {
     options.compilerArgumentProviders.run {
       add {
         listOf(
-            "-source",
-            sourceCompatibility,
-            "-target",
-            targetCompatibility,
+            "--release",
+            options.release.get().toString(),
             "-properties",
             jdtPrefs.toString(),
             "-classpath",

build-logic/src/main/kotlin/com/ibm/wala/gradle/eclipse-maven-central.gradle.kts

@@ -15,6 +15,10 @@ plugins {
 // WALA uses elsewhere.
 java.toolchain.languageVersion = the<EclipseCompatibleJavaExtension>().languageVersion
 
+// When building Eclipse-compatible code, always generate Java 17 bitcode, and assume a Java 17
+// standard library.
+tasks.withType<JavaCompile>().configureEach { options.release = 17 }
+
 /**
  * WALA-specialized adaptation of
  * [ReleaseConfigurer](https://javadoc.io/doc/com.diffplug.gradle/goomph/latest/com/diffplug/gradle/eclipse/MavenCentralExtension.ReleaseConfigurer.html).