Lintian tag for gles packages

[Lisandro Damián Nicanor Pérez Meyer]

tl;dr: I'm asking for review of possible new lintian tags

Hi! As you might now Dmitry added OpenGL ES support for Qt packages:

<https://mitya57.me/weblog/2020/01/qt-opengl-es-packages-available.html>

This leads to a new situation: packages depending upon qtbase5-dev normally
should also conditionally depend upon qtbase5-gles-dev, as per

<https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949028>

This are normally development packages that use Qt.

There are of course some corner cases. If a package is intended to be used with
Desktop OpenGL then depending just on qtbase5-dev is enough. The same analogy
goes for apps using only OpenGL ES.

I think this is a nice case for a lintian tag. I've tried to create one but perl
is definitely not my friend. So I'm planning to file a wishlist bug requesting
for one.

So I'm proposing the following new lintian tags, for which I would like some
review:

Tag: qtbase5-dev-dependency-but-no-gles-option
Severity: normal
Certainty: certain
Check: fields/package-relations
Info: This package depends upon qtbase5-dev but does not adds the
 qtbase5-gles-dev alternative:
 .
 qtbase5-dev | qtbase5-gles-dev
 .
 Note that this tag can be safely overriden if the application is meant to be
 run only in a Desktop OpenGL setup. See #949028 for more information.

Tag: qtbase5-gles-dev-dependency-but-no-desktop-option
Severity: normal
Certainty: certain
Check: fields/package-relations
Info: This package depends upon qtbase5-gles-dev but does not adds the
 qtbase5-dev alternative:
 .
 qtbase5-dev | qtbase5-gles-dev
 .
 Note that this tag can be safely overriden if the application is meant to be
 run only in a OpenGl ES capable setup. See #949028 for more information.