Fix a cctest/test-bytecode-generator/PrivateMethods mismatch between the
PrivateMethods source string and the snippet in the golden file due to
missing newline at the end of the string. Change C++ raw string back to
a normal string since in this case it makes it harder to see the
problem.

Change-Id: I3bea8873d37fbacac65548be8261f6b04104132f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1709413
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62823}