chore: enable flowcheck on CI (#11945)

* chore: enable flowcheck on CI

* fix: flow errors

packages/babel-parser/src/plugins/estree.js

@@ -45,7 +45,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
     estreeParseDecimalLiteral(value: any): N.Node {
       // https://github.com/estree/estree/blob/master/experimental/decimal.md
-      // $FlowIgnore
       // todo: use BigDecimal when node supports it.
       const decimal = null;
       const node = this.estreeParseLiteral(decimal);

packages/babel-parser/src/plugins/placeholders.js

@@ -203,6 +203,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       this.next();
       this.takeDecorators(node);
+      const oldStrict = this.state.strict;
 
       const placeholder = this.parsePlaceholder("Identifier");
       if (placeholder) {
@@ -226,7 +227,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       this.parseClassSuper(node);
       node.body =
         this.parsePlaceholder("ClassBody") ||
-        this.parseClassBody(!!node.superClass);
+        this.parseClassBody(!!node.superClass, oldStrict);
       return this.finishNode(node, type);
     }
 

packages/babel-parser/src/plugins/typescript/index.js

@@ -2727,7 +2727,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return hasContextParam ? baseCount + 1 : baseCount;
     }
 
-    parseCatchClauseParam(): N.Identifier {
+    parseCatchClauseParam(): N.Pattern {
       const param = super.parseCatchClauseParam();
       const type = this.tsTryParseTypeAnnotation();