[SPARK-18677] Fix parsing ['key'] in JSON path expressions.

## What changes were proposed in this pull request?

This fixes the parser rule to match named expressions, which doesn't work for two reasons:
1. The name match is not coerced to a regular expression (missing .r)
2. The surrounding literals are incorrect and attempt to escape a single quote, which is unnecessary

## How was this patch tested?

This adds test cases for named expressions using the bracket syntax, including one with quoted spaces.

Author: Ryan Blue <blue@apache.org>

Closes #16107 from rdblue/SPARK-18677-fix-json-path.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala

@@ -69,7 +69,7 @@ private[this] object JsonPathParser extends RegexParsers {
   // parse `.name` or `['name']` child expressions
   def named: Parser[List[PathInstruction]] =
     for {
-      name <- '.' ~> "[^\\.\\[]+".r | "[\\'" ~> "[^\\'\\?]+" <~ "\\']"
+      name <- '.' ~> "[^\\.\\[]+".r | "['" ~> "[^\\'\\?]+".r <~ "']"
     } yield {
       Key :: Named(name) :: Nil
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/JsonExpressionsSuite.scala

@@ -43,6 +43,30 @@ class JsonExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
       """{"price":19.95,"color":"red"}""")
   }
 
+  test("$['store'].bicycle") {
+    checkEvaluation(
+      GetJsonObject(Literal(json), Literal("$['store'].bicycle")),
+      """{"price":19.95,"color":"red"}""")
+  }
+
+  test("$.store['bicycle']") {
+    checkEvaluation(
+      GetJsonObject(Literal(json), Literal("$.store['bicycle']")),
+      """{"price":19.95,"color":"red"}""")
+  }
+
+  test("$['store']['bicycle']") {
+    checkEvaluation(
+      GetJsonObject(Literal(json), Literal("$['store']['bicycle']")),
+      """{"price":19.95,"color":"red"}""")
+  }
+
+  test("$['key with spaces']") {
+    checkEvaluation(GetJsonObject(
+      Literal("""{ "key with spaces": "it works" }"""), Literal("$['key with spaces']")),
+      "it works")
+  }
+
   test("$.store.book") {
     checkEvaluation(
       GetJsonObject(Literal(json), Literal("$.store.book")),