refactor(@ngtools/webpack): remove support for TypeScript 3.9
refactor(@ngtools/webpack): remove support for TypeScript 3.9

BREAKING CHANGE:

TypeScript 3.9 is no longer supported, please upgrade to TypeScript 4.0.

catull/angular-cli,clydin/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,angular/angular-cli,catull/angular-cli,Brocco/angular-cli,clydin/angular-cli,ocombe/angular-cli,Brocco/angular-cli,catull/angular-cli,angular/angular-cli,ocombe/angular-cli,geofffilippi/angular-cli,angular/angular-cli,angular/angular-cli,geofffilippi/angular-cli,ocombe/angular-cli,geofffilippi/angular-cli,ocombe/angular-cli,Brocco/angular-cli,catull/angular-cli,clydin/angular-cli,Brocco/angular-cli,clydin/angular-cli,ocombe/angular-cli