unify exports behavior

[idoros]

Proposal Description

The current symbols of a stylesheet are mostly automatically exported, until we allow explicit export mode, I suggest we unify the behavior of all symbols.

current issues with import/auto-export symbols:

• class & type selectors are not automatically exported - exporting them shouldn't break anything
• type selector transformation bug: MyElement -> .ns__MyElement - fix(core): imported element transform to class #2603
• imported st-var are not exported to JS - should probably stay the default to keep JS to a minimum and could potentially be explicitly exported when such a feature is available

see playground

related issues:

• escaped css variables exported with escaping to javascript #1932