Streamline dump control options

- Rename `--dump-treei` option to `--dumpi-tree`, which itself is now a
  special case of `--dumpi-<tag>` where tag can be a magic word, or a
  filename
- Control dumping via static `dump*()` functions, analogous to `debug()`
- Make dumping independent of the value of `debug()` (so dumping always
  works even without the debug flag)
- Add separate `--dumpi-graph` for dumping V3Graphs, which is again a
  special case of `--dumpi-<tag>`
- Alias `--dump-<tag>` to `--dumpi-<tag> 3` as before

src/V3CUse.cpp

@@ -32,6 +32,8 @@
 
 #include <set>
 
+VL_DEFINE_DEBUG_FUNCTIONS;
+
 //######################################################################
 
 // Visit within a module all nodes and data types they reference, finding
@@ -106,5 +108,5 @@ void V3CUse::cUseAll() {
         // for each output file and put under that
         CUseVisitor{modp};
     }
-    V3Global::dumpCheckGlobalTree("cuse", 0, v3Global.opt.dumpTreeLevel(__FILE__) >= 3);
+    V3Global::dumpCheckGlobalTree("cuse", 0, dumpTree() >= 3);
 }