[MLIR][Presburger] Make constructors from PresburgerSpace explicit

This patch makes constructors of IntegerRelation, IntegerPolyhedron,
PresburgerRelation, PresburgerSet from PresburgerSpace explicit. This
prevents bugs like:

```
void fun(IntegerRelation a, IntegerRelation b) {
  IntegerPolyhedron c = a.intersect(b);
}
```

Here, `a.intersect(b)` will return `IntegerRelation`, which will be implicitly
converted to `PresburgerSpace` and will use the `PresburgerSpace` constructor
for IntegerPolyhedron. Leading to loss of any constraints in the intersection
of `a` and `b`. After this patch, this will give a compile error.

Reviewed By: arjunp

Differential Revision: https://reviews.llvm.org/D122972

mlir/include/mlir/Analysis/Presburger/IntegerRelation.h

@@ -66,7 +66,7 @@ class IntegerRelation : public PresburgerSpace {
   }
 
   /// Constructs a relation with the specified number of dimensions and symbols.
-  IntegerRelation(const PresburgerSpace &space)
+  explicit IntegerRelation(const PresburgerSpace &space)
       : IntegerRelation(/*numReservedInequalities=*/0,
                         /*numReservedEqualities=*/0,
                         /*numReservedCols=*/space.getNumIds() + 1, space) {}
@@ -567,7 +567,7 @@ class IntegerPolyhedron : public IntegerRelation {
 
   /// Constructs a relation with the specified number of dimensions and
   /// symbols.
-  IntegerPolyhedron(const PresburgerSpace &space)
+  explicit IntegerPolyhedron(const PresburgerSpace &space)
       : IntegerPolyhedron(/*numReservedInequalities=*/0,
                           /*numReservedEqualities=*/0,
                           /*numReservedCols=*/space.getNumIds() + 1, space) {}

mlir/include/mlir/Analysis/Presburger/PresburgerRelation.h

@@ -116,7 +116,8 @@ class PresburgerRelation : public PresburgerSpace {
 protected:
   /// Construct an empty PresburgerRelation with the specified number of
   /// dimension and symbols.
-  PresburgerRelation(const PresburgerSpace &space) : PresburgerSpace(space) {
+  explicit PresburgerRelation(const PresburgerSpace &space)
+      : PresburgerSpace(space) {
     assert(space.getNumLocalIds() == 0 &&
            "PresburgerRelation cannot have local ids.");
   }
@@ -151,7 +152,8 @@ class PresburgerSet : public PresburgerRelation {
 protected:
   /// Construct an empty PresburgerRelation with the specified number of
   /// dimension and symbols.
-  PresburgerSet(const PresburgerSpace &space) : PresburgerRelation(space) {
+  explicit PresburgerSet(const PresburgerSpace &space)
+      : PresburgerRelation(space) {
     assert(space.getNumDomainIds() == 0 && "Set type cannot have domain ids.");
     assert(space.getNumLocalIds() == 0 &&
            "PresburgerRelation cannot have local ids.");