bug#32763: 26.1; emacs-module.h isn't installed with Emacs for module development

[Vasilij Schneidermann]

I've recently developed a simple module and ran into a surprising issue
with the skeleton: I couldn't locate the emacs-module.h in my system
matching the Emacs installation the module is compiled against.  I
eventually gave up and just bundled the emacs-module.h from a Git
checkout with my module's source code.  It makes up for most of the code
in the project.

This is far from ideal.  If I give an Emacs user the source code of a
module without that header file, they can't easily compile it for their
system.  This severely hamper a workflow where a package manager would
be extended to handle module compilation as I haven't found other Emacs
modules bundling the header file.  Is this an oversight in the
installation process or a deliberate design decision?