Revert "Revert "prepare acquireDirect API" - stupid crap"

thought of an idea for optimization. let's try again.

This reverts commit 4ca7033dec.

src/engine/platform/abstract.cpp

@@ -23,6 +23,9 @@
 void DivDispatch::acquire(short** buf, size_t len) {
 }
 
+void DivDispatch::acquireDirect(blip_buffer_t** bb, size_t off, size_t len) {
+}
+
 void DivDispatch::fillStream(std::vector<DivDelayedWrite>& stream, int sRate, size_t len) {
 }
 
@@ -127,6 +130,10 @@ bool DivDispatch::getDCOffRequired() {
   return false;
 }
 
+bool DivDispatch::hasAcquireDirect() {
+  return false;
+}
+
 bool DivDispatch::getWantPreNote() {
   return false;
 }