Refine UX for registering with missing name
## Context On the registration page, errors are displayed in the old style. They should be displayed in the new style of in an input [validation](https://design.gitlab.com/patterns/forms). | Current behavior | Correct behavior | | ------ | ------ | | ![Screen_Shot_2022-12-16_at_12.59.09](/uploads/2598b0a4b4842f7dc8470e37b5e4614b/Screen_Shot_2022-12-16_at_12.59.09.png) | ![Screen_Shot_2022-12-16_at_12.59.13](/uploads/3bc13ae9f08439c71757cb284433c57e/Screen_Shot_2022-12-16_at_12.59.13.png) | | Validation errors are shown on the top of the page | Validation errors are displayed as part of the form element | ## Error copy * First name = `First name is required.` * Last name = `Last name is required.` * Username = `Username is taken.` * Username = `Username is required.` * Email = `Email is taken.` * Email = `Email is required.` * Email = `Enter a valid email address.` * Password = `Password must be at least 8 characters.` * Password = `Password is required.` <details> <summary> Conversations from MR </summary> cc @luzhiyuan.deer From @katiemacoy: > Could you update the error messaging to have form validation? You can read more in our [documentation](https://design.gitlab.com/patterns/forms). > > We will probably want to change the copy as well. Perhaps `Last name is required`. > > We should also make sure other form elements on this page use the same form validation and have similar copy. Let me know what you think. The following discussion from !105013 should be addressed: - [ ] @katiemacoy started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/105013#note_1191827233): (+5 comments) > hey @luzhiyuan.deer @cablett @hmehra I'm happy to do the ~UX review on this one but I'm a bit unclear what I should be checking for. Should I try to save the registration from with the last name missing? </details>
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