[CFE] List pattern without "rest elements" should match lists of exact length

[alexmarkov]

Part of #49749.
This is the reason for the runtime error on co19/LanguageFeatures/Patterns/logical_and_A03_t02 test.

Example:

main() {
  var x = [1, 2];
  if (x case [1]) {
    print('Bug!');
  } else {
    print('OK');
  }
}

Kernel:

  static method main() → dynamic {
    core::List<core::int> x = core::_GrowableList::_literal2<core::int>(1, 2);
    final core::List<core::int> #t1 = x;
    final core::bool #t2 = true;
    final core::List<core::int> #t3 = #t1;
    if(#t3.{core::List::length}{core::int}.{core::num::>=}(1){(core::num) → core::bool}) {
      final dynamic #t4 = #t3{core::List<dynamic>}.{core::List::[]}(0){(core::int) → dynamic};
      if(#t4 =={core::Object::==}{(core::Object) → core::bool} 1) {
        #t2 = false;
        {
          core::print("Bug!");
        }
      }
    }
    if(#t2) {
      core::print("OK");
    }
  }

Note that the list pattern incorrectly checks if x.length >= 1 and not x.length == 1.

/cc @johnniwinther @chloestefantsova