Drop support for template typed slots with defineComponent to reduce a half memory usage

[johnsoncodehk]

For support template typed slots, we need to have 2 TS language services, one of which for bypasses regular DefineComponent type export to resolve #94, this is causes memory usage to double.

But now we already have script setup, support template typed slots with script setup will no have #94 problem, I planed to remove template TS language service instance in @volar/vue-typescript, and change template typed slots to only support for script setup. With regular defineComponent() component definition, you should always use $slots option to define slots type.

Reduce a half memory usage would be a major improvement for volar, but we need to wait for vuejs/core#2693 completed before migrating to the new typed slots implementation, @pikax is there any chance of this being done in the near future?