New issue by fosslinux on void-packages repository

https://github.com/void-linux/void-packages/issues/27735

Description:
There are varying opinions among maintainers in regards to how best to structure `$distfiles`.

For some time there has been an xlint rule that there must not be any variables in `$homepage`, which is good to me. However, when the distfile is contained underneath the homepage, such as for most github projects, there are two conflicting opinions among Void maintainers, namely whether or not to contract/expand `$homepage` in the template. For example, `distfiles=https://github.com/emersion/xdg-desktop-portal-wlr/archive/v${version}.tar.gz` v.s. `distfiles=${homepage}/archive/v$version.tar.gz`.

For a new contributor, this is often very confusing, when one maintainer reviews and asks to shorten/expand and then another maintainer responds with asking not to do this. I have seen this happen many times before, one example being https://github.com/void-linux/void-packages/pull/23296#discussion_r517525903.

To rectify this issue:

1. Add a note to Manual.md on a consensus on what should be done.
2. Create an xlint rule.

(feel free to edit below)

#### Pros for contracting (i.e. using `${homepage}`):

1. Shorter variable declarations
2. Less places to change if upstream moves github, for example.

#### Pros for expanding (i.e. not using `${homepage}`):

1. Easier to copy-paste urls
2. "obfuscates" url

@void-linux/pkg-committers (if i can even do that)