Ng-zorro-antd: Add accessibility/WCAG2/ARIA support

[ttaranov]

Reproduction link

https://escvxj.run.stackblitz.io/

Steps to reproduce

almost all components documented on https://ng.ant.design/components/form/en have web accessibility issues, according to WCAG and ARIA standards:
https://www.w3.org/TR/WCAG21/
https://www.w3.org/TR/wai-aria-1.1/

What is expected?

• add appropriate aria-* roles defined and managed appropriately on actions (e.g. on drop down expand/collapse),
• input items should should have labels (or aria labels)
• keyboard navigation support
• WCAG 2.0 color schemes

What is actually happening?

all required ARIA roles and labels are missing, keyboard and navigation support could be improved

| Environment | Info |
|---|---|
| ng-zorro-antd | 8.5.2 |
| Browser | any |

[wendellhu95]

Support of a11y is listed in our milestone #3667. We would like any help from the community. :heart:

[zorro-bot[bot]]

Hello @ttaranov. We totally like your proposal/feedback, welcome to send us a Pull Request for it. Please fill the Pull Request Template here, provide documentation/test cases if needed and make sure CI passed, we will review it soon. Appreciate it advance and we are looking forward to your contribution!

你好 @ttaranov, 我们完全同意你的提议/反馈，欢迎直接在此仓库 创建一个 Pull Request 来解决这个问题。请务必填写 Pull Request 内的预设模板，提供改动所需相应的测试用例、文档等，并确保 CI 通过，我们会尽快进行 Review，提前感谢和期待您的贡献！

[krokofant]

@ttaranov @wendellhu95 How much of this should be handled by Ng-Zorro and how much should be handle by the consumer?

Is it an issue specific to the docs? Consumers can add aria labels to their inputs and adjust their themes. I imagine some aria attributes are harder for the consumer to specify.

[wendellhu95]

@krokofant The React version could be a good reference. They already have aria-* supported.

[estellechvl]

would really love this to be implemented. Also focus trap on submenus.

[krokofant]

The above PR is stale and probably won't get any updates. If someone want's to pick it up it's encouraged.