[MLIR][Printing] ASMPrinter prints escape characters in Resources

[AndrewZhaoLuo]

Summary

In https://reviews.llvm.org/D157928 ellison of printing resources was added.
In the refactor, the proper printing of escape characters was mistakenly removed.
This patch adds it back in and adds a small unit test.

[AndrewZhaoLuo]

cc @Mogball @jpienaar

mlir/lib/IR/AsmPrinter.cpp

public:
     ResourceBuilder(PrintFn printFn) : printFn(printFn) {}
     ~ResourceBuilder() override = default;
 
     void buildBool(StringRef key, bool data) final {
       printFn(key, [&](raw_ostream &os) { os << (data ? "true" : "false"); });
     }
 
     void buildString(StringRef key, StringRef data) final {
-      printFn(key, [&](raw_ostream &os) { os << "\"" << data << "\""; });
+      printFn(key, [&](raw_ostream &os) {
+        os << "\"";
+        llvm::printEscapedString(data, os);
+        os << "\"";
+      });
     }
 
     void buildBlob(StringRef key, ArrayRef<char> data,
                    uint32_t dataAlignment) final {
       printFn(key, [&](raw_ostream &os) {
         // Store the blob in a hex string containing the alignment and the data.
         llvm::support::ulittle32_t dataAlignmentLE(dataAlignment);
         os << "\"0x"

mlir/test/IR/pretty-resources-print.mlir

 // Check printing with --mlir-elide-resource-strings-if-larger elides printing large resources
 
 // RUN: mlir-opt %s --mlir-elide-resource-strings-if-larger=10| FileCheck %s
 
 // To ensure we print the resource keys, have reference to them
 // CHECK: attr = dense_resource<blob1> : tensor<3xi64>
 "test.blob1op"() {attr = dense_resource<blob1> : tensor<3xi64> } : () -> ()
 
 // CHECK-NEXT: attr = dense_resource<blob2> : tensor<3xi64>
 "test.blob2op"() {attr = dense_resource<blob2> : tensor<3xi64> } : () -> ()
 
 // CHECK:      {-#
 // CHECK-NEXT:   external_resources: {
 // CHECK-NEXT:     external: {
 // CHECK-NEXT:       bool: true,
-// CHECK-NEXT:       string: "string"
+// CHECK-NEXT:       string: "\22string\22"
 // CHECK-NEXT:     },
 // CHECK-NEXT:     other_stuff: {
 // CHECK-NEXT:       bool: true
 // CHECK-NEXT:     }
 // CHECK-NEXT:   }
 // CHECK-NEXT: #-}
 
 {-#
   dialect_resources: {
     builtin: {
       blob1: "0x08000000010000000000000002000000000000000300000000000000",
       blob2: "0x08000000040000000000000005000000000000000600000000000000"
     }
   },
   external_resources: {
     external: {
       blob: "0x08000000010000000000000002000000000000000300000000000000",
       bool: true,
-      string: "string"
+      string: "\"string\"" // with escape characters
     },
     other_stuff: {
       bool: true
     }
   }
 #-}