feat: add override keyword

[HerrCai0907]

fix: #2353
add override keyword and type check

support following code

class A {
  method(): void {}
}
class B extends A {
  override method(): void {}
  // This member cannot have an 'override' modifier because it is not declared in the base class 'A'.
  override method_error(): void {}
}

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[MaxGraey]

Thanks!