Create a ECJ version of BlazeJavaCompilerPlugin

[guw]

The Bazel javac compiler supports plugins via BlazeJavaCompilePlugin. We need to create a version of this, which allows integration with ECJ.

Specifically the following two methods are offered by BlazeJavaCompilePlugin:

/**
 * Performs analysis actions after the attribute phase of the javac compiler. The attribute phase
 * performs symbol resolution on the parse tree.
 *
 * @param env The attributed parse tree (after symbol resolution)
 */
public void postAttribute(Env<AttrContext> env) {}

/**
 * Performs analysis actions after the flow phase of the javac compiler. The flow phase performs
 * dataflow checks, such as finding unreachable statements.
 *
 * @param env The attributed parse tree (after symbol resolution)
 */
public void postFlow(Env<AttrContext> env) {}

This work also includes patching ECJ to allow contributing such plug-ins programmatically.