Fix type files geneartion to export only types

[RayRedGoose]

🐛 Bug Report

The type definition files output assignment which is not legal in definitions files. TypeScript definition files (*.d.ts) only declare types and do not assign values. It is a subtle difference, but the = should be changed to : and the as const removed.

Expected Behavior

// es6/system/index.d.ts
export declare const color: {
  bg: {
    "default": "--cnvs-sys-color-bg-default",
    // ...
  },
  // ...
};

// es6/base/index.d.ts
export declare const cinnamon100: "--cnvs-base-palette-cinnamon-100";

Actual Behavior

// es6/system/index.d.ts
export declare const color = {
  bg: {
    "default": "--cnvs-sys-color-bg-default",
    // ...
  } as const,
  // ...
} as const;

// es6/base/index.d.ts
export declare const cinnamon100 = "--cnvs-base-palette-cinnamon-100";