[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

     }
 
     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,

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
+// RUN: mlir-opt %s --mlir-elide-resource-strings-if-larger=20| FileCheck %s
 
 // To ensure we print the resource keys, have reference to them
 // CHECK: attr = dense_resource<blob1> : tensor<3xi64>

 // 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

     external: {
       blob: "0x08000000010000000000000002000000000000000300000000000000",
       bool: true,
-      string: "string"
+      string: "\"string\"" // with escape characters
     },
     other_stuff: {
       bool: true