Type guards can't deal with unknown type as default

We can't know the failures of type inference in type guards because of this problem. Maybe `a is any[]` should also return unknown[]. <!-- Please try to reproduce the issue with the latest published version. It may have already been fixed. For npm: `typescript@next` This is also the 'Nightly' version in the playground: http://www.typescriptlang.org/play/?ts=Nightly --> **TypeScript Version:** 3.7.x-dev.20200410 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** **Code** ```ts declare function f(a: any): a is any[]; declare function g(a: any): a is unknown[]; declare const a: readonly number[]; f(a) && a; // any[] g(a) && a; // not unknown[] ``` **Expected behavior:** a's type narrowed by g is `unknown[]`. **Actual behavior:** a's type narrowed by g is `readonly number[] & unknown[]`. **Playground Link:** https://www.typescriptlang.org/play/?ts=3.9.0-dev.20200410&ssl=1&ssc=1&pln=6&pc=11#code/CYUwxgNghgTiAEAzArgOzAFwJYHtVIAooAueKVATwEpSp4sBnMygbQF0BuAKFElgRTpseeAHMitSjTL0maANaocAd1TtuvaHHhg8DDGVJwowPBArxUyALYAjEDHVcuiIlXgAyD2W7io7rx8gA **Related Issues:** #17002