add es6 deprecation messages to some utils, remove duplicated utils, https://github.com/microsoft/vscode/issues/90676

Array accesses are not strict null checked. Added a type checked helper for when you just want to get the first element of an array of fallback to a default if the array is empty

The type system should catch these now

coalesce does not mutate its input array

Use `Array<T | U>` when dealing with union types instead of  `(T | U)[]`

This negation of `isFalsyOrEmpty` works better for type guards. After the check, you know that you have an array with at least one element

Using an overload makes the code more complex and prevents  patterns such as `.then(coalesce)` or `.map(coalesce)`. It also makes it clear which code paths are actually being most used in our code

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header

* Seed random shuffle of extension recommendations

* Documentation