Parser: corpus parse rate 69% -> 81%, and stop --tests from sticking

Grammar: 'using,except(x)' modifiers, '#ifx' with block branches, unions with
parameters, multi-value initializers, mixed 'name:, lvalue = call()' targets,
'push_context' with no explicit context, 'operator []=', '#foreign lib "symbol"',
keyword-named arguments such as 'remove={...}', and '#insert (options) body'.
Directive flags now require adjacency: without it, in
'(callback: (*GUID) #c_call, lpContext: *void)' the flag swallowed ', lpContext'.

procModifier is now just directiveExpr — one rule for directives in both
positions, so fixes apply everywhere.

jaitest: a '--tests' filter persisted through Gradle's configuration cache, so a
later unfiltered ./jaitest silently re-ran only that class and printed OK.
Unfiltered runs now disable the configuration cache.

MIN_CLEAN_FILES ratchets the corpus gate at 575/714.

src/main/gen/dev/hgh/jai/psi/impl/JaiPushContextStatementImpl.java

@@ -34,9 +34,9 @@ public class JaiPushContextStatementImpl extends ASTWrapperPsiElement implements
   }
 
   @Override
-  @NotNull
+  @Nullable
   public JaiExpr getExpr() {
-    return findNotNullChildByClass(JaiExpr.class);
+    return findChildByClass(JaiExpr.class);
   }
 
 }