New rules for linting type declarations

[ghost]

We've been working on lint rules for DefinitelyTyped and most may be of general use. Would you be interested in my making PRs for some of these rules?

Name	Description	PR
forbidden-types	This forbids the Function, Object, Boolean, Number, and String types. These have better alternatives (specific function types, {}, boolean, number, string).	#2271
functional-interfaces	This prefers type Foo = () => void over interface Foo { (): void; }.	#1891
interface-over-type-literal	This prefers interface Foo { x: number; } over type Foo = { x: number; }.	#1890
no-empty-interface	This forbids interface Foo { }. (TypeScript is structurally typed, so this doesn't accomplish anything.)	#1889
no-public	This forbids the public keyword. This could be an option for member-access to make it forbid instead of mandate.	#2247
unified-signatures	This prefers `interface Foo { foo(x: number	string): void; }overinterface Foo { foo(x: number): void; foo(x: string): void; }`.
void-return	This forbids foo(x: void): number but allows foo(x: number): void. This could be joined with forbidden-types.	N/A

(dt-header and no-single-declare-module will probably not be useful outside of DefinitelyTyped.)

[nchen63]

Name	Description
forbidden-types	👍 Integrate into ban rule or rename to ban-type
functional-interfaces	👍 I like it
interface-over-type-literal	👍 I like it
no-empty-interface	👍 I like it
no-public	🤔 I don't see the benefit of this one
unified-signatures	How would this work for more complex signatures like interface Foo { foo(x: number, y: boolean): void; foo(x: string, y: SomeInterface): void; }? Would it allow a bad combo like foo(true, "bar")?.
void-return	I don't understand why someone would write foo(x: void): number in the first place

[adidahiya]

I don't think the ban rule covers anything in type positions

[nchen63]

right, I'll edit the table

[ghost]

With #2273 this should be done.