Promise能否增加基于点(.)语法的链式写法支持？用 [] 来写链式写法步骤多了之后超级别扭啊

**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.

Review the existing Promise API and its current []-based chaining usage in coobjc. Determine the intended dot-syntax behavior and whether the request is still relevant; done would require an agreed design and documented, working dot-based chaining support.

Written by the indexing model from the issue text.