feat!: redesign icons

[sxyazi]

Goals:

• Improve Matching Performance: The newly introduced dirs, files, and exts compile the icon rules into a HashMap at startup. This allows most icon matches to be completed with O(1) complexity, significantly enhancing matching performance.
• Built-in nvim-web-devicons: This includes a richer and ready-to-use set of icons out of the box.
• Enhanced Icon Styling: Each icon now supports specifying both dark and light colors (currently only fg_dark is used). In the future, the terminal color will automatically choose the appropriate color. This is added as part of Enable live update of flavor through Lua plugin API #988.
• Enhanced is Function: The original is functionality has been reimplemented as conds to allow more complex conditional expressions, such as cond = "!dir & exec".