Add JDK 8 `tools.jar` contents to bootclasspath

Copybara Import from https://github.com/bazelbuild/rules_java/pull/183

BEGIN_PUBLIC
Add JDK 8 `tools.jar` contents to bootclasspath (#183)

Work towards https://github.com/bazelbuild/bazel/issues/21771

Closes #183
END_PUBLIC

COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_java/pull/183 from fmeum:patch-2 89b7b38addba626ecbafc19d1cca56eedf85bdc8
PiperOrigin-RevId: 622197442
Change-Id: Id91213454dd9f7b18d926114816b245bbad74fe3

toolchains/DumpPlatformClassPath.java

diff --git a/toolchains/DumpPlatformClassPath.java b/toolchains/DumpPlatformClassPath.java
index 4707e89..17b014a 100644
--- a/toolchains/DumpPlatformClassPath.java
+++ b/toolchains/DumpPlatformClassPath.java
@@ -187,6 +187,10 @@
         jars.add(path);
       }
     }
+    Path toolsJar = javaHome.resolve("lib/tools.jar");
+    if (Files.exists(toolsJar)) {
+      jars.add(toolsJar);
+    }
     return jars;
   }