feat(common): Add an 'outlet' injector option for ngTemplateOutlet

[mmalerba]

Adds an option (ngTemplateOutletInjector="outlet") that instructs the ngTemplateOutlet to inherit its injector from the outlet's place in the instantiated DOM.

[JeanMeche]

Question: could this be a fix for #54097 ?

[mmalerba]

Hmm I don't think so, the template outlet in that example looks like its already manually doing something pretty similar to what this would do. I tried adding an extra Injector.create to that example and it still had the same issue, so I think it would have the same issue with "inherit". This change was motivated by making it easier to build recursive structures like this: https://stackblitz.com/edit/stackblitz-starters-9csxbu?file=src%2Fmain.ts

[mmalerba]

@alxhub couple questions for you to make sure I'm on the right track

[mmalerba]

I'm not really sure why I need to create a child injector instead of just passing along the current injector, but based on my stackblitz testing it did seem to be necessary. Just wanted to call that out in case I'm doing something wrong

[alxhub]

It shouldn't be necessary I don't think...

[mmalerba]

Here's a modified version of my stackblitz to show that it really does seem to need me to create a child to get the same behavior as composing with content projection: https://stackblitz.com/edit/stackblitz-starters-9csxbu?file=src%2Fmain.ts

[mmalerba]

I talked to @crisbeto about this. He says this behavior makes sense to him because embedded view injectors can't be injected using inject(Injector). By creating the child injector, we create an injector that acts as an embedded injector, but it ends up consulting the node injector for each lookup.