Introduce a new key `generated_buffers`, which
stores an array of generated buffers. These
include the buffer text, as well as its original
location and any parent buffers.
While here, also fix rdar://107281079 such that
only apply the filename fallback logic to the
pretty-printed Decl case. We ought to remove this
fallback once the editor can handle it though.
rdar://107281079
rdar://107952288
The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
The quoting of the sed commands was creating problems in my Windows
installation. I am unsure if the implementation of sed.exe is different
or the cmd.exe is different.
In order to avoid problems in different machines, replace the piped sed
commands into only one python script. This should be multiplatform and
should execute the same in any of them. It also remove a lot of the
extra quoting and escaping, and avoids 5 processes for only just one.
