docs(language-service): update integration test information (#32269)
docs(language-service): update integration test information (#32269)

The documentation for the langauge service plugin integration test
appears to be stale. Remove section about new versions of TypeScript,
which appear not to be tested, and update the information about
generating and updating goldens to reflect the new way of doing so.
Add information about install deps in the repo root, this directory, and
building Angular before testing.

Also remove trailing whitespace on one line.

PR Close #32269

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