[BUG] regexp_replace with replacement string containing \ can produce incorrect results

[andygrove]

Describe the bug
There are differences in behavior between CPU and GPU in some cases when using regexp_replace and a replacement string that contains the backslash character,

The expression regexp_replace(strings,'[a-z]+','\\\\WORD') will replace matches with WORD on the CPU and with \WORD on the GPU.

Steps/Code to reproduce bug

Add this test to RegularExpressionsSuite.scala

testSparkResultsAreEqual("String regexp_replace with backslash ",
  extractStrings, conf = conf) {
  frame => frame.selectExpr("regexp_replace(strings,'[a-z]+','\\\\WORD')")
}

Expected behavior
Behavior should be consistent between CPU and GPU.

Environment details (please complete the following information)
N/A

Additional context
None