Adds helpers for extracting original name of a lowered late field, the
original initializer and the field used to hold the value of the lowered
field.
This helps backends to customize late field encoding while still using
the lowering provided by the cfe.
Change-Id: Ib42af539efad84a08a6e32acd29d2efaff129cd7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/178989
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Johnni Winther