goose: use readable variable names

Names are inferred from types most of the time, but have a fallback for
a non-named type. Names are now also disambiguated from symbols in the
same scope.

Reviewed-by: Tuo Shan <shantuo@google.com>
Reviewed-by: Herbie Ong <herbie@google.com>

internal/goose/testdata/NoInjectParamNames/foo/foo.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	stdcontext "context"
+	"fmt"
+	"os"
+)
+
+type context struct{}
+
+func main() {
+	c, err := inject(stdcontext.Background(), struct{}{})
+	if err != nil {
+		fmt.Println("ERROR:", err)
+		os.Exit(1)
+	}
+	fmt.Println(c)
+}
+
+//goose:provide
+
+func provide(ctx stdcontext.Context) (context, error) {
+	return context{}, nil
+}