Cache some LS calls in fourslash (#19517)
Cache some LS calls in fourslash (#19517)

* Cache some LS calls in fourslash

* Add comment

minestarks/TypeScript,kitsonk/TypeScript,alexeagle/TypeScript,microsoft/TypeScript,microsoft/TypeScript,SaschaNaz/TypeScript,donaldpipowitch/TypeScript,kpreisser/TypeScript,donaldpipowitch/TypeScript,TukekeSoft/TypeScript,weswigham/TypeScript,minestarks/TypeScript,RyanCavanaugh/TypeScript,weswigham/TypeScript,Microsoft/TypeScript,Microsoft/TypeScript,SaschaNaz/TypeScript,nojvek/TypeScript,SaschaNaz/TypeScript,RyanCavanaugh/TypeScript,basarat/TypeScript,nojvek/TypeScript,alexeagle/TypeScript,weswigham/TypeScript,Microsoft/TypeScript,kitsonk/TypeScript,RyanCavanaugh/TypeScript,basarat/TypeScript,kpreisser/TypeScript,basarat/TypeScript,nojvek/TypeScript,minestarks/TypeScript,microsoft/TypeScript,kpreisser/TypeScript,TukekeSoft/TypeScript,SaschaNaz/TypeScript,basarat/TypeScript,kitsonk/TypeScript,alexeagle/TypeScript,donaldpipowitch/TypeScript,TukekeSoft/TypeScript,donaldpipowitch/TypeScript,nojvek/TypeScript