Support const assertions equivalent

[amatiasq]

TypeScript has this feature called "const assertions" where we can ask the type system to interpret the values as literal (1, "test", true...) instead of their type (number, string and boolean respectively).

This avoids code duplication:

const foo = {
  test: 1,
  bar: "quz",
} as const;

type FooType = typeof foo;

/*
type FooType = {
    readonly test: 1;
    readonly bar: "quz";
}
*/

TS Playground

Related to #186