Allow readonly arrays with strictTemplates enabled

[dev054]

🐞 bug report

Is this a regression? No.

Description

Currently we can't pass readonly string[] to dropSpecialCharacters and specialCharacters with strictTemplates enabled.

🔬 Minimal Reproduction

<!-- Argument of type 'readonly [...]' is not assignable to parameter of type 'string[]'.
  The type 'readonly [...]' is 'readonly' and cannot be assigned to the mutable type 'string[]'. ->
<input matInput formControlName="test" mask="testing" [specialCharacters]="specialCharacters">

specialCharacters = ['[', ']', '\\'] as const;

🌍 Your Environment

Angular Version: 10.x.

Anything else relevant? To solve this we can do the following:

ngx-mask/projects/ngx-mask-lib/src/lib/config.ts

Lines 13 to 14 in f14b4fe

	dropSpecialCharacters: boolean | string[];
	specialCharacters: string[];

- dropSpecialCharacters: boolean | string[];
- specialCharacters: string[];
+ dropSpecialCharacters: boolean | readonly string[];
+ specialCharacters: readonly string[];

[andriikamaldinov1]

@dev054 Thanks for using Ngx-mask. Pls update to latest version.
It example all work as expected - https://stackblitz.com/edit/stackblitz-starters-epnjbs?file=src%2Fmain.ts