[v2] NSIS installer support for Windows (#1184)

* [v2] Add support for post build hooks

Currently only supports build-level hooks

* [v2] Improve build assets handling and use single source for manifest generation

The manifest asset files are now a go template and data will be
resolved before they are included into the build output.

Breaking Change: Windows manifest file must be named
“wails.exe.manifest” and doesn’t depend on the project name
anymore.

* [v2, windows] NSIS installer generation

v2/internal/system/system_linux.go

@@ -45,6 +45,13 @@ func (i *Info) discover() error {
 					dep.Version = locallyInstalled.Version
 				}
 			}
+			if dep.Name == "nsis" {
+				locallyInstalled := checkNSIS()
+				if locallyInstalled.Installed {
+					dep.Installed = true
+					dep.Version = locallyInstalled.Version
+				}
+			}
 		}
 		i.Dependencies = dependencies
 	}