…property-feature-extraction

- feature file `/features/css-custom-property.ts`
- moved `CSSVarSymbol` symbol
- export empty diagnostics and hooks
- register to stylable meta class

- moved all code related to feature file
- new `analyzeDeclaration` feature hook

- `isCSSVarProp` from `stylable-utils` to `helpers/css-custom-property`
- `validateAllowedNodesUntil` from `stylable-value-parser` to `helpers/value`
- `globalValue` from `utils` to `helpers/global`
- deprecate `paramMapping` constant export

- analyze `@st-global-custom-property` to feature
- add `toRemove` api to `analyzeAtRule` feature until `rawAst` is immutable

- `transformResolve`
- `transformAtRule`
- `transformJSExports`

- `transformDeclarationValue` new hook
- transform `var()` extract from `functions` to feaure
- `stringifyFunction` from `functions` to `helpers/value`

- `transformDeclaration` - move `--X: ;` namespace to feature
- `getScopedCSSVar` from `transformer` to `helpers/css-custom-property`
- deprecate `transformer.getScopedCSSVar()`

…property-feature-extraction

- refactored to new format with inline tests and `testStylableCore`
- add internal `CSSCustomProperty.get(symbolName)`

- `exports.spec` css custom property tests
- test for resolving mixed-in property override
- moved skipped escape test

- add `alias` field to `CSSVarSymbol` to point to imported symbol
- implemented suppurt for aliased in resolver and completion-provider
- register `--` prefixed imports as aliased custom property symbols
- sort conflicted symbol definitions from import, `@property`, and `@st-custom-global-property`

- import path and file name didn't match

- keep `var()` untransformed
- report empty prop name diagnostic

…property-feature-extraction