build: add imports for go generate tools (#24682)

This adds a tools.go file to import all command packages used for
go:generate. Doing so makes it possible to execute go-based code
generators using 'go run', locking in the tool version using go.mod.

Co-authored-by: Felix Lange <fjl@twurst.com>

signer/fourbyte/4byte.go

@@ -147000,6 +147000,9 @@ var _bindata = map[string]func() (*asset, error){
 	"4byte.json": _4byteJson,
 }
 
+// AssetDebug is true if the assets were built with the debug flag enabled.
+const AssetDebug = false
+
 // AssetDir returns the file names below a certain
 // directory embedded in the file by go-bindata.
 // For example if you run go-bindata on data/... and data contains the