package kit: Add pre-uninstall scripts feature.

Just like post-install scripts which run shortly after a package is
installed, pre-uninstall scripts are run just before a package is
removed. Implements enhancement #13427

* Fix script exit code handling vs script launch errors.
* Bump package and repo file version numbers due to new attribute,
unfortunately makes new .hpkg files not backwards compatible.
* Add pre-uninstall functionality, mostly cloning the post-install
except in a few places.
* Discover that _RunQueuedScripts() is never called, a future TODO:?
* Update package documentation for pre-uninstall scripts, and use of
the boot/post-install directory.

Change-Id: I45596255ce74bc102f6e5b606cbf83e4e4347a17
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1504
Reviewed-by: Alexander G. M. Smith <agmsmith@ncf.ca>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

Repository file format: group attributes of a package

* Introduce new package attribute B_HPKG_ATTRIBUTE_ID_PACKAGE (valid
only in a repository file) to group the attributes belonging to a
package.
* BRepositoryContentHandler:
- No longer derive from BPackageContentHandler.
- Add hooks HandlePackage() and HandlePackageDone() that bracket the
attributes for a package. This is more explicit and robust than
handlers having to guess when one package ended and the next began.
* BRepositoryCache: Make use of BPackageInfoContentHandler. No need to
duplicate the code for reading a package info from package info
attributes.

hpkg format: Generalize user/global settings file attributes

* For all identifiers: Rename global settings file to global writable
file. We want to use the respective attribute also for other writable
files, not only settings files.
* User settings file/global writable file info/attribute: Add
isDirectory property/child attribute. This allows declaring global/
user settings directories associated with the package.

hpkg format: Add attribute for declaring post install scripts

hpkg format: Add attributes for declaring users and groups

Move package attribute ID definitions to a separate file

... <package/hpkg/PackageAttributes.h>, which also defines other
properties (name and type) for each attribute. It does so via a macro
that the caller can define to generate whatever code is desired.

Repository file format: group attributes of a package

* Introduce new package attribute B_HPKG_ATTRIBUTE_ID_PACKAGE (valid
only in a repository file) to group the attributes belonging to a
package.
* BRepositoryContentHandler:
- No longer derive from BPackageContentHandler.
- Add hooks HandlePackage() and HandlePackageDone() that bracket the
attributes for a package. This is more explicit and robust than
handlers having to guess when one package ended and the next began.
* BRepositoryCache: Make use of BPackageInfoContentHandler. No need to
duplicate the code for reading a package info from package info
attributes.

hpkg format: Generalize user/global settings file attributes

* For all identifiers: Rename global settings file to global writable
file. We want to use the respective attribute also for other writable
files, not only settings files.
* User settings file/global writable file info/attribute: Add
isDirectory property/child attribute. This allows declaring global/
user settings directories associated with the package.

hpkg format: Add attribute for declaring post install scripts

hpkg format: Add attributes for declaring users and groups

Move package attribute ID definitions to a separate file

... <package/hpkg/PackageAttributes.h>, which also defines other
properties (name and type) for each attribute. It does so via a macro
that the caller can define to generate whatever code is desired.