`VerbAttribute` has unnecessary breaking changes between 2.8.0 and 2.9.1

**Describe the bug**
`VerbAttribute`'s constructor signature has changed between 2.8.0 and 2.9.1. There is a default value for the new alias parameter, so recompilation of the same source code is possible without error. However, upgrading without rebuilding is not possible.

**To Reproduce**
Steps to reproduce the behavior:
1. Create an exe depending on CommandLineParser 2.8.0 that uses `VerbAttribute`
2. Replace CommandLineParser 2.8.0 with CommandLineParser 2.9.1 in the bin folder
3. Execute the exe
4. See error

**Additional context**
When having multiple exes in the same folder, all exes need to be rebuilt and updated simultaneously along with updating CommandLineParser in order to upgrade.

Reintroducing the 2.8.0 `VerbAttribute` constructor, (and possibly labeling it as obsolete), would allow assemblies built with version 2.8.0 and assemblies built with version 2.9.1 to both work with the new version (possibly requiring binding redirects).

先在 C# 專案中找出 VerbAttribute 建構函式，並在不重新建置可執行檔的情況下，重現從 CommandLineParser 2.8.0 升級至 2.9.1 的已回報問題。檢查 VerbAttribute 或組件相容性相關的現有測試，然後確保針對這兩個版本建置的組件都能搭配較新的套件執行，而不會發生已回報的建構函式錯誤。

由索引模型根據 Issue 內容生成。