[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/webview2runtime/webview2installer.go

@@ -0,0 +1,21 @@
+package webview2runtime
+
+import (
+	_ "embed"
+	"os"
+	"path/filepath"
+)
+
+//go:embed MicrosoftEdgeWebview2Setup.exe
+var setupexe []byte
+
+// WriteInstallerToFile writes the installer file to the given file.
+func WriteInstallerToFile(targetFile string) error {
+	return os.WriteFile(targetFile, setupexe, 0755)
+}
+
+// WriteInstaller writes the installer exe file to the given directory and returns the path to it.
+func WriteInstaller(targetPath string) (string, error) {
+	installer := filepath.Join(targetPath, `MicrosoftEdgeWebview2Setup.exe`)
+	return installer, WriteInstallerToFile(installer)
+}