feat: support Rule.rules (nested rules) (#1618)

Author: opl-

Diff for: lib/plugin-webpack4.js

@@ -146,6 +146,10 @@ function cloneRule (rule) {
     }
   })
 
+  if (rule.rules) {
+    res.rules = rule.rules.map(cloneRule)
+  }
+
   if (rule.oneOf) {
     res.oneOf = rule.oneOf.map(cloneRule)
   }

Diff for: lib/plugin-webpack5.js

@@ -182,6 +182,10 @@ function cloneRule (rawRule, refs) {
 
   delete res.test
 
+  if (rawRule.rules) {
+    res.rules = rawRule.rules.map(rule => cloneRule(rule, refs))
+  }
+
   if (rawRule.oneOf) {
     res.oneOf = rawRule.oneOf.map(rule => cloneRule(rule, refs))
   }