Add Mica Alt support (#17650)

[typenoob]

Summary of the Pull Request

1. Changing the existing $theme.$window.useMica property in the settings from a straight boolean to a string enum $theme.$window.micaStyle

• "default" (stands for not using mica)
• "original" (stands for using original mica)
• "alt" (stands for using mica alt)

2. Implement mica alt by using DWMSBT_TABBEDWINDOW in DWM_SYSTEMBACKDROP_TYPE enumeration

References and Relevant Issues

#17650

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

Change $theme.$window.micaStyle property in the setting.json, see the performances of the window theme

• "default" (performs the same as useMica=false)
• "original" (performs the same as useMica=true)
• "alt" (performs Mica Alt theme)

PR Checklist

• Closes #xxx
• Tests added/passed
• Documentation updated
  • If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated (if necessary)

[typenoob]

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