Makes behaviour of changing leading indent or trailing newlines opt-in.
There are only slightly more uses of this method that don't want this (now opt-in) behaviour, although I think this is slightly less surprising (for example the trailing newline behaviour was to "add a trailing newline only if it didn't already exist" which I don't think was obvious).
Mostly this was just changing the defaults and all of the call sites. However, some call sites were getting the old behaviour (inc leading/trailing whitespace), but then calling `.trim()`, so I didn't add the opt-in there because it would then be removed (they won't show up in the diff because they didn't actually get any changes).
Change-Id: I2f05b3a6266aaad5ee510ce2a8bf269b26d42d5d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/329540
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Danny Tuppeny
cf78037c5b