Move utility functions to common functions

[MAILPOET-2677]

assets/js/src/common/functions/change_handlers.ts

@@ -0,0 +1,8 @@
+import { ChangeEvent } from 'react';
+
+type Setter = (value: string) => any
+type Event = ChangeEvent<any>
+
+export const onChange = (setter: Setter) => (e: Event) => setter(e.target.value);
+
+export const onToggle = (setter: Setter) => (e: Event) => setter(e.target.checked ? '1' : '0');

assets/js/src/common/functions/index.ts

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+export * from './change_handlers';
+export { default as t } from './t';
+export { default as isEmail } from './is_email';

assets/js/src/common/functions/is_email.ts

@@ -0,0 +1 @@
+export default (value: string): boolean => (window as any).mailpoet_email_regex.test(value);

assets/js/src/common/functions/t.ts

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+import MailPoet from 'mailpoet';
+
+export default ([word]: TemplateStringsArray) => MailPoet.I18n.t(word);