This reverts commit e7c6dea to re-land the previous change in #29773.
Chinmay realized that because we link the whole engine into one DLL on Windows, the export settings for the symbols don't affect this code: If we include a second copy of the double-conversion library, the duplicate symbols are all internal to the DLL. Consequently, we need to link to the copy in the Dart runtime, so this is the correct implementation. If the Dart team decides to change/remove the library in the future, we will need to add in our own copy at that time.
This adds some accessibility improvements for reading out numbers. Currently this code is only used on Windows.
6079aa5f81