feat(ngcc): support --async flag (defaults to true) (#33192)
feat(ngcc): support --async flag (defaults to true) (#33192)

This allows disabling parallelism in ngcc if desired, which is mainly useful
for debugging. The implementation creates the flag and passes its value to
mainNgcc.

No tests are added since the feature mainly exists already - ngcc supports
both parallel and serial execution. This commit only allows switching the
flag via the commandline.

PR Close #33192

vikerman/angular,snaptech/angular,StephenFluin/angular,blesh/angular,manekinekko/angular,alxhub/angular,matsko/angular,vikerman/angular,Toxicable/angular,brandonroberts/angular,wKoza/angular,brandonroberts/angular,sarunint/angular,wKoza/angular,vikerman/angular,matsko/angular,blesh/angular,angular-indonesia/angular,gdi2290/angular,mhevery/angular,shairez/angular,blesh/angular,IdeaBlade/angular,gdi2290/angular,mgechev/angular,manekinekko/angular,mgechev/angular,manekinekko/angular,ocombe/angular,mprobst/angular,JiaLiPassion/angular,JiaLiPassion/angular,ocombe/angular,StephenFluin/angular,mgechev/angular,mgechev/angular,Brocco/angular,StephenFluin/angular,gnomeontherun/angular,alxhub/angular,ocombe/angular,alxhub/angular,ocombe/angular,Toxicable/angular,angular/angular,filipesilva/angular,gkalpak/angular,angular/angular,gkalpak/angular,filipesilva/angular,vikerman/angular,filipesilva/angular,IdeaBlade/angular,Brocco/angular,JiaLiPassion/angular,filipesilva/angular,brandonroberts/angular,IdeaBlade/angular,Toxicable/angular,JiaLiPassion/angular,gdi2290/angular,shairez/angular,Brocco/angular,gnomeontherun/angular,angular-indonesia/angular,manekinekko/angular,alxhub/angular,alxhub/angular,snaptech/angular,sarunint/angular,snaptech/angular,wKoza/angular,vikerman/angular,mgechev/angular,brandonroberts/angular,gnomeontherun/angular,mhevery/angular,gnomeontherun/angular,brandonroberts/angular,sarunint/angular,IdeaBlade/angular,sarunint/angular,manekinekko/angular,mprobst/angular,matsko/angular,matsko/angular,snaptech/angular,Brocco/angular,snaptech/angular,angular-indonesia/angular,Toxicable/angular,StephenFluin/angular,mprobst/angular,matsko/angular,mhevery/angular,mprobst/angular,mhevery/angular,blesh/angular,StephenFluin/angular,mhevery/angular,Brocco/angular,angular-indonesia/angular,shairez/angular,snaptech/angular,shairez/angular,IdeaBlade/angular,vikerman/angular,wKoza/angular,gkalpak/angular,sarunint/angular,gdi2290/angular,shairez/angular,wKoza/angular,gkalpak/angular,gdi2290/angular,gdi2290/angular,blesh/angular,Brocco/angular,ocombe/angular,mhevery/angular,ocombe/angular,brandonroberts/angular,wKoza/angular,filipesilva/angular,angular/angular,manekinekko/angular,Toxicable/angular,Toxicable/angular,mprobst/angular,mprobst/angular,angular/angular,sarunint/angular