Conditional member access for map children?

[lukepighetti]

Any chance we can add conditional member access for map children?

Example:

Today it works like this

Map coolMap = {
  'foo':'bar'
};

final thing = coolMap['baz']['broke'] // error

Tomorrow it works like this?

Map coolMap = {
  'foo':'bar'
};

final thing = coolMap?.['baz']?.['broke'] // null

[natebosch]

Closing as a duplicate of #28389