* Modernize gradle buildscript

* Bump yarn/loader/fabric api versions

* Add GH actions to build example mod

* Update in response to feedback

* Ignore commonly generated Mac OS junk files

This is optional, but it would be a huge quality of life improvement for anyone developing on Mac OS, as the first thing I do when starting a new project is always to add this to the .gitignore. Example: Just from the small changes I've made to the build script alone, I've generated 4 .DS_Store files, which would clutter up this PR if I included them.

* Simply processResources logic & make it compatible with future versions of Gradle

When the processResources task is currently run, it uses deprecated Gradle features. Running "gradle clean build --warning-mode all" should output a message along the lines of "Copying or archiving duplicate paths with the default duplicates strategy has been deprecated. This is scheduled to be removed in Gradle 7.0.". This is due to inlcuding all files twice, as the "from" blocks includes them for the second time (gradle includes these files by default). This PR simply edits the relevant files from the already selected resources directory. This also reduces the amount of repetition in the script.

* Switch to double quotes to match style

D'oh!

* Add minVersion to mixin config

* Bump loader dep requriement to >=0.7.4

Co-authored-by: modmuss50 <modmuss50@gmail.com>

Sadly this bug snuck into previous versions, this has been fixed.

Update Yarn mappings to 1.14.1+build.5

Yarn 1.14.1+build.4 had an issue with Hopper#getWorld being renamed to Hopper#getHopperWorld, which caused the world to crash when ticking hoppers in dev. 1.14.1+build.5 fixed this, but the example mod wasn't updated yet, so anyone following the dev install instructions on the site would run into the issue.

Update to fabric 0.2.6.121