Create .gitignore for Flax Engine

FlaxEngine.gitignore

+# Ignore Flax project files
+Binaries/
+Cache/
+Logs/
+Output/
+Screenshots/
+*.HotReload.*
+
+# Ignore Visual Studio project files (generated locally)
+*.csproj
+*.sln
+
+# Ignore thumbnails created by Windows
+Thumbs.db
+
+# Ignore files built by Visual Studio
+*.obj
+*.exe
+*.pdb
+*.user
+*.aps
+*.pch
+*.vspscc
+*_i.c
+*_p.c
+*.ncb
+*.suo
+*.tlb
+*.tlh
+*.bak
+*.cache
+*.ilk
+*.log
+[Bb]in
+[Dd]ebug*/
+*.lib
+*.sbr
+obj/
+[Rr]elease*/
+_ReSharper*/
+[Tt]est[Rr]esult*
+.vs/
+
+# Ignore Nuget packages folder
+packages/