Add Angle & Length constraint/value, and modal for the details (#54)

* setup UI for getting length and Angle values from user

* enable setLength-angle for angledLines with an exisiting constraining value

src/lang/queryAst.ts

@@ -135,7 +135,7 @@ export function getNodePathFromSourceRange(
   return path
 }
 
-interface PrevVariable<T> {
+export interface PrevVariable<T> {
   key: string
   value: T
 }