Unity with new Premake scripts!

Using the new premake scripts to build the native unity plugin, look at all those redundant files go bye bye!

Diffs=
6150f1267 Unity with new Premake scripts! (#6532)

Co-authored-by: Luigi Rosso <luigi-rosso@users.noreply.github.com>

.rive_head

diff --git a/.rive_head b/.rive_head
index 1d4a985..f8c3357 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-231b35a4130d96ee9be540f51b82c0ef831bad91
+6150f1267c5bd8e480358f2c8786910ad180df55

build/rive_build_config.lua

diff --git a/build/rive_build_config.lua b/build/rive_build_config.lua
index 30608af..296a235 100644
--- a/build/rive_build_config.lua
+++ b/build/rive_build_config.lua
@@ -322,11 +322,13 @@
     filter({ 'system:macosx', 'options:arch=arm64 or arch=universal' })
     do
         buildoptions({ '-arch arm64' })
+        linkoptions({ '-arch arm64' })
     end
 
     filter({ 'system:macosx', 'options:arch=x64 or arch=universal' })
     do
         buildoptions({ '-arch x86_64' })
+        linkoptions({ '-arch x86_64' })
     end
 
     filter({