Changed AppStream ID to rDNS-style to match what's on Flathub

[Pointedstick]

Resolves #2103

[TingPing]

I think we might as well go all the way and rename the actual desktop file.

[Pointedstick]

Your commit doesn't actually fix the problem of mismatched AppStream IDs. You didn't get rid of the trailing .desktop part, so the ID still doesn't match Flathub, which uses io.github.Hexchat.

HexChat's AppStream ID here should likewise be io.github.Hexchat.

[TingPing]

The Flathub package does use io.github.Hexchat.desktop though?

<component type="desktop">
  <id>io.github.Hexchat.desktop</id>
  <provides>
    <id>hexchat.desktop</id>
  </provides>

[Pointedstick]

Let me see if we can handle this in Discover, or maybe even AppStream.

[TingPing]

I'll remove the .desktop if appstream recommends it (I pinged hughsie about that in another bug) but I do think this is an issue elsewhere in the stack.

[Pointedstick]

We do currently handle this case in Discover, but FWIW, it's not in conformance with the AppStream Spec: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#sect-Metadata-GenericComponent

The <id> tag is a unique identifier for this component. It must contain only ASCII characters, dots, hyphens and numbers. Spaces are not allowed.
The ID must follow a reverse-DNS scheme, consisting of {tld}.{vendor}.{product}, for example org.kde.Gwenview or com.hugski.ColorHug2. Ownership of {vendor}.{tld} in the domain name system guarantees uniqueness of IDs.