Applications: Properly parse desktop exec keys and stop shelling out

[sents]

https://specifications.freedesktop.org/desktop-entry-spec/latest/exec-variables.html describes how commands and their arguments are stored in the exec key. As the exec key is a string type as defined in https://specifications.freedesktop.org/desktop-entry-spec/latest/value-types.html escapes code for certain characters have to be respected. After this there are rules which characters necessitate a quoted string and which characters need to be escaped in a quoted string. To use the exec key for executing we then need to unescape these characters and can collect the args in a vector. This enables us to stop shelling out when executing desktop files and instead call Command directly with the specified program and arguments.

[pope]

I just want to +1 this, as it's been sitting here a while. I have run into cases where the error in parsing means that .desktop files don't work.