Java: Rename integration test directories.

We are no longer bound to the platform-specific directories, so simplify the test organization.
If you don't want this change, just skip merging this PR. It's purely optional.

I kept the platform-specific directories around under `kotlin`,
but you could also easily merge all these together if you find them unhelpful.
I'll leave that change to you.

java/ql/integration-tests/java/buildless-module-definition-not-in-module-info-file/PrintAst.expected

@@ -0,0 +1,3 @@
+Test2.java:
+#    0| [CompilationUnit] Test2
+#    1|   1: [Class] Test2

java/ql/integration-tests/java/buildless-module-definition-not-in-module-info-file/PrintAst.qlref

@@ -0,0 +1 @@
+semmle/code/java/PrintAst.ql

java/ql/integration-tests/java/buildless-module-definition-not-in-module-info-file/Test.java

@@ -0,0 +1 @@
+module mymodule { }

java/ql/integration-tests/java/buildless-module-definition-not-in-module-info-file/Test2.java

@@ -0,0 +1 @@
+public class Test2 { }

java/ql/integration-tests/java/buildless-module-definition-not-in-module-info-file/test.py

@@ -0,0 +1,4 @@
+def test(codeql, java):
+    codeql.database.create(
+        extractor_option="buildless=true",
+    )