docs: clarify providedIn options (#42355)
docs: clarify providedIn options (#42355)

The list for the possible options of providedIn was not totally clear. This commit ensures each possible value is included explicitly in the docs.

fixes #29330

PR Close #42355

mgechev/angular,manekinekko/angular,gkalpak/angular,shairez/angular,manekinekko/angular,ocombe/angular,mgechev/angular,gkalpak/angular,brandonroberts/angular,brandonroberts/angular,ocombe/angular,ocombe/angular,angular-indonesia/angular,angular/angular,gnomeontherun/angular,angular-indonesia/angular,JiaLiPassion/angular,manekinekko/angular,gnomeontherun/angular,brandonroberts/angular,mgechev/angular,gkalpak/angular,angular-indonesia/angular,brandonroberts/angular,shairez/angular,shairez/angular,angular/angular,ocombe/angular,angular-indonesia/angular,JiaLiPassion/angular,manekinekko/angular,brandonroberts/angular,ocombe/angular,shairez/angular,manekinekko/angular,brandonroberts/angular,ocombe/angular,manekinekko/angular,angular/angular,JiaLiPassion/angular,angular/angular,gkalpak/angular,mgechev/angular,gnomeontherun/angular,gnomeontherun/angular,JiaLiPassion/angular,mgechev/angular,shairez/angular