fix(plugin): load desktop entries from user dir

[oknozor]

Currently the destkop-entry plugin retains the entries emitted by the freedesktop-desktop-entry crate in reverse order.

For instance '$HOME/.local/share/applications/jetbrains-clion.desktop' is emitted first then overriden by '/usr/share/applications/jetbrains-clion.desktop'.

Instead of Hashset::replace, Hashset::insert must be use to avoid overriding entries with higher priority.

From freedesktop basedir specification:

• " There is a set of preference ordered base directories relative to which data files should be searched. This set of directories is defined by the environment variable $XDG_DATA_DIRS." (see: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html)

From desktop-entries specification:

• "If multiple files have the same desktop file ID, the first one in the $XDG_DATA_DIRS precedence order is used." (see: https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html)