Add generator blueprint for prototype extensions

[dwickern]

We should generate a .d.ts with prototype extensions.

Prototype extensions are controlled by EXTEND_PROTOTYPES:
https://guides.emberjs.com/v2.3.0/configuring-ember/disabling-prototype-extensions/

We can't conditionally enable types based on this so the best we can do is generate a .d.ts which the user can edit.

Array prototype extensions should be enabled by default for apps and disabled for addons. Function prototype extensions should be disabled by default probably. We haven't implemented string prototype extensions.

declare global {
    interface Array<T> extends Ember.ArrayPrototypeExtensions<T> {}
    interface Function extends Ember.FunctionPrototypeExtensions {}
}

[dfreeman]

Function prototype extensions should be disabled by default probably.

AFAIK array prototype extensions are the only ones that aren't already deprecated/slated for deprecation, so it makes sense to me that they'd be the only ones enabled by default.

[dwickern]

Can a blueprint detect if it's an addon vs. app for the array prototype extensions?

[dfreeman]

In most cases yes, though the addon story for e-c-ts is a little bit of an oddball, since having it as a devDependency means it's technically only installed for the addon's dummy app. We may have to settle for checking if the project name is dummy and basing the decision on that (or the presence of an addon/ directory, or any number of other good-enough hacks)

[chriskrycho]

Looking at what I have for this in #108 and the discussion above: it looks like the function prototype extensions should probably be included but commented out to make it easy for people to “flip a switch” and turn them on?

[AvremelM]

Just a heads up: enabling interface Function extends Ember.FunctionPrototypeExtensions { } causes typing errors when using ember-decorators' class decorators for me.

[ts] Unable to resolve signature of class decorator when called as an expression. Type 'Function' is not assignable to type 'void | typeof Badge'. Type 'Function' is not assignable to type 'typeof TooltipBadge'.

Hope this helps anyone coming across that issue.