Exclude dev files from dist package

[cedric-anne]

For the time being, when fetching the dist package from composer, all repository files are included.
Using export-ignore git attribute would permit to make the dist package ligther (see https://php.watch/articles/composer-gitattributes#export-ignore).

Ignore files weight: 195.5kB
Remaining files weight: 128.2kB

[michelf]

My objection to this is it will also affect the archives you can download from GitHub.

[cedric-anne]

It could also be done by adding a archive.exclude property in composer.json. Do you want me to update this PR with this solution ?

[michelf]

Sounds like a good idea.

[cedric-anne]

Done.

[michelf]

Thank you.