[analysis_server] Improve re-indenting of fixes/assists + add additional switch expression fix for Wrap

The original goal of this change was to add the `switchExpression` test in `flutter_wrap_center_test.dart`, but it failed on Windows and exposed a bug that affected a number of assists/fixes.

The issue was that indentation was being rewritten using a regex:

src.replaceAll(RegExp('^$indentOld', multiLine: true), indentNew)

On Windows, when `indentOld` is an empty string, both `\r` and `\n` are matched individually, resulting in indentation being inserted between them:

foo\r    \n    bar

To fix this, I changed all places using a regex for replacement like this to call the existing `CorrectionUtils.replaceSourceIndent` method which did not have this problem. However, it made two different assumptions:

1. Indentation should always be updated on the first line (which if `indentOld` is an empty string, results in extra unwanted indentation being prepended to the string)
2. A new EOL should always be added at the end of the new code

To handle this, I added two new parameters and kept the original behaviour the same (although, I'm not sure if defaulting to adding a newline makes a lot of sense).

Change-Id: Ifa714da62c2541ba54a5376aa67149c90396dec2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/328220
Reviewed-by: Keerti Parthasarathy <keertip@google.com>
Commit-Queue: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>