refactor(elements): simplify accessing `NgElementStrategy` (#36114)
refactor(elements): simplify accessing `NgElementStrategy` (#36114)

Previously, we had to check whether `NgElementStrategy` had been
instantiated before accessing it. This was tedious and error prone,
since it was easy to forget to add the check in new call sites.

This commit switches to using a getter, so that the check has to be
performed in one place and is transparent to call sites (including any
future ones).

PR Close #36114

IdeaBlade/angular,filipesilva/angular,JiaLiPassion/angular,manekinekko/angular,angular/angular,manekinekko/angular,alxhub/angular,manekinekko/angular,gdi2290/angular,angular-indonesia/angular,gkalpak/angular,alxhub/angular,gkalpak/angular,filipesilva/angular,mgechev/angular,shairez/angular,wKoza/angular,IdeaBlade/angular,alxhub/angular,ocombe/angular,IdeaBlade/angular,angular-indonesia/angular,manekinekko/angular,mgechev/angular,IdeaBlade/angular,IdeaBlade/angular,mgechev/angular,filipesilva/angular,brandonroberts/angular,ocombe/angular,angular/angular,gdi2290/angular,angular/angular,wKoza/angular,angular-indonesia/angular,gnomeontherun/angular,shairez/angular,gkalpak/angular,gdi2290/angular,gdi2290/angular,mgechev/angular,ocombe/angular,wKoza/angular,gkalpak/angular,filipesilva/angular,JiaLiPassion/angular,alxhub/angular,gdi2290/angular,wKoza/angular,shairez/angular,brandonroberts/angular,wKoza/angular,JiaLiPassion/angular,shairez/angular,blesh/angular,angular-indonesia/angular,wKoza/angular,brandonroberts/angular,brandonroberts/angular,mgechev/angular,ocombe/angular,brandonroberts/angular,brandonroberts/angular,blesh/angular,blesh/angular,manekinekko/angular,angular/angular,JiaLiPassion/angular,ocombe/angular,gdi2290/angular,manekinekko/angular,gnomeontherun/angular,blesh/angular,shairez/angular,gnomeontherun/angular,blesh/angular,filipesilva/angular,ocombe/angular,alxhub/angular,gnomeontherun/angular