IR: Give 'DI' prefix to debug info metadata

Finish off PR23080 by renaming the debug info IR constructs from `MD*`
to `DI*`.  The last of the `DIDescriptor` classes were deleted in
r235356, and the last of the related typedefs removed in r235413, so
this has all baked for about a week.

Note: If you have out-of-tree code (like a frontend), I recommend that
you get everything compiling and tests passing with the *previous*
commit before updating to this one.  It'll be easier to keep track of
what code is using the `DIDescriptor` hierarchy and what you've already
updated, and I think you're extremely unlikely to insert bugs.  YMMV of
course.

Back to *this* commit: I did this using the rename-md-di-nodes.sh
upgrade script I've attached to PR23080 (both code and testcases) and
filtered through clang-format-diff.py.  I edited the tests for
test/Assembler/invalid-generic-debug-node-*.ll by hand since the columns
were off-by-three.  It should work on your out-of-tree testcases (and
code, if you've followed the advice in the previous paragraph).

Some of the tests are in badly named files now (e.g.,
test/Assembler/invalid-mdcompositetype-missing-tag.ll should be
'dicompositetype'); I'll come back and move the files in a follow-up
commit.

llvm-svn: 236120
diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
index 652851f..6c517f5 100644
--- a/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -285,7 +285,7 @@
 
 ValueEnumerator::ValueEnumerator(const Module &M,
                                  bool ShouldPreserveUseListOrder)
-    : HasMDString(false), HasMDLocation(false), HasGenericDebugNode(false),
+    : HasMDString(false), HasDILocation(false), HasGenericDINode(false),
       ShouldPreserveUseListOrder(ShouldPreserveUseListOrder) {
   if (ShouldPreserveUseListOrder)
     UseListOrders = predictUseListOrder(M);
@@ -382,7 +382,7 @@
 
         // Don't enumerate the location directly -- it has a special record
         // type -- but enumerate its operands.
-        if (MDLocation *L = I.getDebugLoc())
+        if (DILocation *L = I.getDebugLoc())
           EnumerateMDNodeOperands(L);
       }
   }
@@ -548,8 +548,8 @@
     EnumerateValue(C->getValue());
 
   HasMDString |= isa<MDString>(MD);
-  HasMDLocation |= isa<MDLocation>(MD);
-  HasGenericDebugNode |= isa<GenericDebugNode>(MD);
+  HasDILocation |= isa<DILocation>(MD);
+  HasGenericDINode |= isa<GenericDINode>(MD);
 
   // Replace the dummy ID inserted above with the correct one.  MDValueMap may
   // have changed by inserting operands, so we need a fresh lookup here.