tools: Never generate webpack dependencies to files outside of the project
tools: Never generate webpack dependencies to files outside of the project

webpack's file dependencies include files in the project directory's
parent dir [1]. This is dangerous and broken, and broke releases
with commit 8c68b1ed85: As cockpituous' release-source clones the
project into a ./source.XXXX tmp dir, there now suddenly existed a
../package.json file which got included into the webpack compiler stats'
`fileDependencies`, and thus generated a bogus "../package.json" file
dependency. This would not exist in actual build environments (such as
rpm builds), and broke package builds.

Avoid this by requiring that all generated dependencies live inside of
the project.

[1] https://github.com/webpack/webpack/issues/14481

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