This reverts commit f80411d8.

Remove NavigationToolbar condition that leading widget cannot be larger than 1/3 the total space available. (#112548)

Update FileImage to use the new ImmutableBuffer.fromFilePath constructor to avoid loading bytes through the Dart heap. As a side effect, tis fixes #112881 which prevents dart:io from opening a file larger than INT_MAX bytes on windows.

For files that are not exactly a dart:io file, we still use the old method of calling loadBytes() in order to not make this a breaking change.