Locates a conventional temporary directory to be associated with a workspace.
This directory is suitable for temporary files to be deleted later in the course of a build,
or caches and local repositories which should persist across builds done in the same workspace.
(If multiple workspaces are present for a single job built concurrently, via
#allocate(FilePath), each will get its own temporary directory.)
It may also be used for security-sensitive files which
DirectoryBrowserSupport ought not serve,
acknowledging that these will be readable by builds of other jobs done on the same node.
Each plugin using this directory is responsible for specifying sufficiently unique subdirectory/file names.
FilePath#createTempFile may be used for this purpose if desired.
The resulting directory may not exist; you may call
FilePath#mkdirs on it if you need it to.
It may be deleted alongside the workspace itself during cleanup actions.