[Types] Some missing type declarations

[KiddoV]

There are a few missing and wrong type declarations throughout all modules. I’m taking note of them, and once I have enough, I will create a PR for it.

Dropdown

Missing:

{
        /**
         * Clears the remote api cache once.
         */
        (behavior: 'clear cache'): JQuery;
}

Dropdown.DropdownSettings

Missing:

{
        /**
         * Whether search selection will force currently selected choice when element is blurred.
         * If a 'select' tag with a required attribute was used, the 'forceSelection' setting will be set to 'true' automatically.
         * @default false
         */
        forceSelection: boolean;
}

Wrong declaration:

{
        onNoResults(searchValue: string): boolean; //<== change `void` to `boolean`
        
        onSearch(): void | false; //<== this should return `void or false`
}

---

Form

Wrong signature:

{
        /**
         * Validates field, updates UI, and calls 'onSuccess' or 'onFailure'.
         */
        (behavior: 'validate field', fieldName: string): boolean; //<= return `boolean` not `void`

        /**
         * Sets key/value pairs from passed values object to matching identifiers.
         */
        (behavior: 'set values', values: object): JQuery; //<= `values` should be `object` not `object[]`
}

All Modules

Wrong declaration:

{
        /**
         * Callback after popup is hidden.
         */
        onHidden(this: JQuery, element?: JQuery<HTMLElement>): void;}
        
        //Some callback should return `element` as HTMLElement instead of JQuery<HTMLElement>. Need to check on all callbacks again!

More to come...

[KiddoV]

@lubber-de can you add this issue to milestone 2.9.4?
Thanks!