Implement more detailed symbol info for tags with slot-related attributes

[sethidden]

• I have searched through existing issues

Feature Request

1. Show slots in vscode symbol browser:
   

2. Show slot[name="slotname"] in symbol search instead of just slot in symbol search

Things I'm not sure about:

• Should old slot & slot-scope syntax be supported?
• Displaying the slot like div#id.class #slotname is weird as two attrs use the # symbol (which is normally reserved for id). Maybe div#id.class[#slotname] would be better? VSCode never returns attr info for symbols in .html files though (eg. <input type='number'> still returns symbol info like input rather than input[type='number']
• Should slot syntax be unified in symbols? eg. should symbol search always show template[#slot] even though the user explicitly wrote <template v-slot:slot> in code?

Rationale

Consider this case where you have a large component with many slots. You may want to quickly jump between slots using the symbol search (CTRL+SHIFT+O).