[fir][NFC] Move fir.shape verifier to cpp file

[clementval]

Summary

Move verifier code to the .cpp file.

Follow up to https://reviews.llvm.org/D110626.

This patch is part of the upstreaming effort from fir-dev branch.

flang/include/flang/Optimizer/Dialect/FIROps.td

def fir_ShapeOp : fir_Op<"shape", [NoSideEffect]> {
   let arguments = (ins Variadic<AnyIntegerType>:$extents);
 
   let results = (outs fir_ShapeType);
 
   let assemblyFormat = [{
     operands attr-dict `:` functional-type(operands, results)
   }];
 
-  let verifier = [{
-    auto size = extents().size();
-    auto shapeTy = getType().dyn_cast<fir::ShapeType>();
-    assert(shapeTy && "must be a shape type");
-    if (shapeTy.getRank() != size)
-      return emitOpError("shape type rank mismatch");
-    return mlir::success();
-  }];
+  let verifier = "return ::verify(*this);";
 
   let extraClassDeclaration = [{
     std::vector<mlir::Value> getExtents() {
       return {extents().begin(), extents().end()};
     }
   }];
 }
 

flang/lib/Optimizer/Dialect/FIROps.cpp

for (decltype(count) i = 0; i != count; ++i) {
     if (!(attr.isa<fir::ExactTypeAttr>() || attr.isa<fir::SubclassAttr>() ||
           attr.isa<mlir::UnitAttr>()))
       return op.emitOpError("invalid type-case alternative");
   }
   return mlir::success();
 }
 
 //===----------------------------------------------------------------------===//
+// ShapeOp
+//===----------------------------------------------------------------------===//
+
+static mlir::LogicalResult verify(fir::ShapeOp &op) {
+  auto size = op.extents().size();
+  auto shapeTy = op.getType().dyn_cast<fir::ShapeType>();
+  assert(shapeTy && "must be a shape type");
+  if (shapeTy.getRank() != size)
+    return op.emitOpError("shape type rank mismatch");
+  return mlir::success();
+}
+
+//===----------------------------------------------------------------------===//
 // ShapeShiftOp
 //===----------------------------------------------------------------------===//
 
 static mlir::LogicalResult verify(fir::ShapeShiftOp &op) {
   auto size = op.pairs().size();
   if (size < 2 || size > 16 * 2)
     return op.emitOpError("incorrect number of args");
   if (size % 2 != 0)