fix(update): support $persist_dir in uninstaller.script

[linsui]

$persist_dir in uninstaller.script only works when uninstall but not when update.

[Ash258]

I do not see a reason to add internal variable, which is not used anywhere.

You have access to almost all core functions from manifests code blocks. And adding $persist_dir = persistdir $app $global is not something really critical you need to hack over tons of lines or escape lots of quotes. It is simple one liner.

[linsui]

It is useful when some files need to be persist manully. $persist_dir is available in uninstaller.script when uninstall but not when update, which is confusing. I didn't notice this problem because I test a manifest by uninstall and install.

[Ash258]

I see what you mean. Yeath this could go in for small period of time.

I am currently working on #2952, which will cover this use case. (#3708)

[Ash258]

@r15ch13, @rasa Could you please fast patch this to develop and sync to master?