Summary:
This changeset moves the creation of the transform cache at the top-level of the bundler so that:
* we can use alternative folders, such as the project path itself, that I think will be more robust especially for OSS;
* we can disable the cache completely, that is useful in some cases (for example, the script that fills the global cache).
The reasons I believe a local project path is more robust are:
* there are less likely conflicts between different users and different projects on a single machine;
* the cache is de facto cleaned up if you clone a fresh copy of a project, something I think is desirable;
* some people have been reporting that `tmpDir` just returns nothing;
* finally, it prevents another user from writing malicious transformed code in the cache into the shared temp dir—only people with write access to the project have write access to the cache, that is consistent.
Reviewed By: davidaurelio
Differential Revision: D5113121
fbshipit-source-id: 74392733a0be306a7119516d7905fc43cd8c778e
a4badb8471