message: refactor(forms): remove unnecessary `!` operators from validators
  When we added the strict null checks, the lexer had some `!` operators added to prevent the compilation from failing.
  See
  PR Close
diff: @@ -158,10 +158,8 @@ export const CHECKBOX_REQUIRED_VALIDATOR: StaticProvider = {
  host: {'[attr.required]': 'required ? "" : null'}
  })
  export class RequiredValidator implements Validator {
  - // TODO(issue/24571): remove '!'.
  - private _required!: boolean;
  - // TODO(issue/24571): remove '!'.
  - private _onChange!: () => void;
  + private _required = false;
  + private _onChange?: () => void;
  /**
  * @description
  @@ -274,10 +272,8 @@ export const EMAIL_VALIDATOR: any = {
  providers: [EMAIL_VALIDATOR]
  })
  export class EmailValidator implements Validator {
  - // TODO(issue/24571): remove '!'.
  - private _enabled!: boolean;
  - // TODO(issue/24571): remove '!'.
  - private _onChange!: () => void;
  + private _enabled = false;
  + private _onChange?: () => void;
  /**
  * @description
  @@ -368,17 +364,15 @@ export const MIN_LENGTH_VALIDATOR: any = {
  host: {'[attr.minlength]': 'minlength ? minlength : null'}
  })
  export class MinLengthValidator implements Validator, OnChanges {
  - // TODO(issue/24571): remove '!'.
  - private _validator!: ValidatorFn;
  - // TODO(issue/24571): remove '!'.
  - private _onChange!: () => void;
  + private _validator: ValidatorFn = Validators.nullValidator;
  + private _onChange?: () => void;
  /**
  * @description
  * Tracks changes to the the minimum length bound to this directive.
  */
  - // TODO(issue/24571): remove '!'.
  - @Input() minlength!: string|number;
  + @Input()
  + minlength!: string|number; // This input is always defined, since the name matches selector.
  /**
  * @description
  @@ -456,17 +450,15 @@ export const MAX_LENGTH_VALIDATOR: any = {
  host: {'[attr.maxlength]': 'maxlength ? maxlength : null'}
  })
  export class MaxLengthValidator implements Validator, OnChanges {
  - // TODO(issue/24571): remove '!'.
  - private _validator!: ValidatorFn;
  - // TODO(issue/24571): remove '!'.
  - private _onChange!: () => void;
  + private _validator: ValidatorFn = Validators.nullValidator;
  + private _onChange?: () => void;
  /**
  * @description
  * Tracks changes to the the maximum length bound to this directive.
  */
  - // TODO(issue/24571): remove '!'.
  - @Input() maxlength!: string|number;
  + @Input()
  + maxlength!: string|number; // This input is always defined, since the name matches selector.
  /**
  * @description
  @@ -547,17 +539,15 @@ export const PATTERN_VALIDATOR: any = {
  host: {'[attr.pattern]': 'pattern ? pattern : null'}
  })
  export class PatternValidator implements Validator, OnChanges {
  - // TODO(issue/24571): remove '!'.
  - private _validator!: ValidatorFn;
  - // TODO(issue/24571): remove '!'.
  - private _onChange!: () => void;
  + private _validator: ValidatorFn = Validators.nullValidator;
  + private _onChange?: () => void;
  /**
  * @description
  * Tracks changes to the pattern bound to this directive.
  */
  - // TODO(issue/24571): remove '!'.
  - @Input() pattern!: string|RegExp;
  + @Input()
  + pattern!: string|RegExp; // This input is always defined, since the name matches selector.
  /**
  * @description
  