Ant task to automatically convert to a simple shim layout

CONTRIBUTING.md

@@ -186,22 +186,38 @@ The following acronyms may appear in directory names:
 |cdh    |Cloudera CDH|321cdh |Cloudera CDH Spark based on Apache Spark 3.2.1|
 
 The version-specific directory names have one of the following forms / use cases:
-- `src/main/312/scala` contains Scala source code for a single Spark version, 3.1.2 in this case
-- `src/main/312+-apache/scala`contains Scala source code for *upstream* **Apache** Spark builds,
+
+#### Version range directories
+
+The following source directory system is deprecated. See below and [shimplify.md][1]
+
+* `src/main/312/scala` contains Scala source code for a single Spark version, 3.1.2 in this case
+* `src/main/312+-apache/scala`contains Scala source code for *upstream* **Apache** Spark builds,
    only beginning with version Spark 3.1.2, and + signifies there is no upper version boundary
    among the supported versions
-- `src/main/311until320-all` contains code that applies to all shims between 3.1.1 *inclusive*,
+* `src/main/311until320-all` contains code that applies to all shims between 3.1.1 *inclusive*,
 3.2.0 *exclusive*
-- `src/main/pre320-treenode` contains shims for the Catalyst `TreeNode` class before the
+* `src/main/pre320-treenode` contains shims for the Catalyst `TreeNode` class before the
   [children trait specialization in Apache Spark 3.2.0](https://issues.apache.org/jira/browse/SPARK-34906).
-- `src/main/post320-treenode` contains shims for the Catalyst `TreeNode` class after the
+* `src/main/post320-treenode` contains shims for the Catalyst `TreeNode` class after the
   [children trait specialization in Apache Spark 3.2.0](https://issues.apache.org/jira/browse/SPARK-34906).
 
 For each Spark shim, we use Ant path patterns to compute the property
 `spark${buildver}.sources` in [sql-plugin/pom.xml](./sql-plugin/pom.xml) that is
 picked up as additional source code roots. When possible path patterns are reused using
 the conventions outlined in the pom.
 
+#### Simplified version directory structure
+
+Going forward new shim files should be added under:
+
+* `src/main/spark${buildver}`, example: `src/main/spark330db`
+* `src/test/spark${buildver}`, example: `src/test/spark340`
+
+with a special shim descriptor as a Scala/Java comment. See [shimplify.md][1]
+
+[1]: ./docs/dev/shimplify.md
+
 ### Setting up an Integrated Development Environment
 
 Our project currently uses `build-helper-maven-plugin` for shimming against conflicting definitions of superclasses
@@ -238,7 +254,12 @@ Known Issues:
 
 * There is a known issue that the test sources added via the `build-helper-maven-plugin` are not handled
 [properly](https://youtrack.jetbrains.com/issue/IDEA-100532). The workaround is to `mark` the affected folders
-such as `tests/src/test/320+-noncdh-nondb` manually as `Test Sources Root`
+such as
+
+  * `tests/src/test/320+-noncdh-nondb`
+  * `tests/src/test/spark340`
+
+manually as `Test Sources Root`
 
 * There is a known issue where, even after selecting a different Maven profile in the Maven submenu,
 the source folders from a previously selected profile may remain active. As a workaround,