Narrow HTMLElement autocapitalize to supported keywords

[Copilot]

HTMLElement.autocapitalize was typed as string, allowing misspelled keywords and preventing custom elements from declaring the platform-defined union.

• DOM declarations

  • Narrow autocapitalize to "off" | "none" | "on" | "sentences" | "words" | "characters".

• Regression coverage

  • Verify all supported keywords are accepted.
  • Verify misspellings such as "character" are rejected.

declare const element: HTMLElement;

element.autocapitalize = "characters"; // accepted
element.autocapitalize = "character";  // error

• Fixes autocapitalize type is incorrect according to MDN #54372

[Jake Bailey (jakebailey)]

This is a generated file