feat(@angular-devkit/core): respect FORCE_COLOR env var behavior

Currently, there is no mechanism in the Angular tooling to forcefully
output colors regardless of detected terminal capabilities. This commit
adds an override via an environment variable: `FORCE_COLOR`. The
behavior in this commit is the same as the behavior in a commonly used
module, `supports-color` (https://github.com/chalk/supports-color#info).
This is especially useful when piping output from the Angular CLI, which
would automatically and irreversibly disable colors before this commit.

Author: imhoffd

packages/angular_devkit/core/src/terminal/caps.ts

@@ -75,8 +75,15 @@ export interface StreamCapabilities {
 
 const ciVars = ['TRAVIS', 'CIRCLECI', 'APPVEYOR', 'GITLAB_CI'];
 
+function _getColorLevel(stream: Socket): 0 | 1 | 2 | 3 {
+  if ('FORCE_COLOR' in _env) {
+    if (_env.FORCE_COLOR === '1') {
+      return 3;
+    } else if (_env.FORCE_COLOR === '0') {
+      return 0;
+    }
+  }
 
-function _getColorLevel(stream: Socket): number {
   if (stream && !stream.isTTY) {
     return 0;
   }