[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.

(cherry picked from commit 48778976)
Signed-off-by: Herman van Hovell <hvanhovell@databricks.com>