[ADT] Adjust parameter names for DenseMap constructors (NFC) (#158501)

This patch ensures that both DenseMap and SmallDenseMap have:

  explicit DenseMap(unsigned NumElementsToReserve = 0) {
    init(NumElementsToReserve);
  }

for consistency and clarity (modulo the class name, of course).

llvm/include/llvm/ADT/DenseMap.h

diff --git a/llvm/include/llvm/ADT/DenseMap.h b/llvm/include/llvm/ADT/DenseMap.h
index b478ce2..e13a2cb 100644
--- a/llvm/include/llvm/ADT/DenseMap.h
+++ b/llvm/include/llvm/ADT/DenseMap.h
@@ -710,9 +710,11 @@
   unsigned NumBuckets;
 
 public:
-  /// Create a DenseMap with an optional \p InitialReserve that guarantee that
-  /// this number of elements can be inserted in the map without grow()
-  explicit DenseMap(unsigned InitialReserve = 0) { init(InitialReserve); }
+  /// Create a DenseMap with an optional \p NumElementsToReserve to guarantee
+  /// that this number of elements can be inserted in the map without grow().
+  explicit DenseMap(unsigned NumElementsToReserve = 0) {
+    init(NumElementsToReserve);
+  }
 
   DenseMap(const DenseMap &other) : BaseT() {
     init(0);
@@ -887,8 +889,8 @@
   AlignedCharArrayUnion<BucketT[InlineBuckets], LargeRep> storage;
 
 public:
-  explicit SmallDenseMap(unsigned NumElementsToReservre = 0) {
-    init(NumElementsToReservre);
+  explicit SmallDenseMap(unsigned NumElementsToReserve = 0) {
+    init(NumElementsToReserve);
   }
 
   SmallDenseMap(const SmallDenseMap &other) : BaseT() {