Enable composite builds.

Few additional tricks are required:
1) Due to resolveJsonModule being true, we need to explicitly add json files to "include" (microsoft/TypeScript#25636)
2) "clean" script must remove *.tsbuildinfo files when deleting build artifacts (otherwise build will be skipped)

Author: aeremin

.gitignore

@@ -65,3 +65,4 @@ api-docs/
 
 # Idea
 .idea
+*.tsbuildinfo

package.json

@@ -14,7 +14,7 @@
     "build:apidocs": "lb-apidocs",
     "build": "lb-tsc es2017 --outDir dist",
     "build:watch": "lb-tsc --watch",
-    "clean": "lb-clean dist",
+    "clean": "lb-clean dist && rm tsconfig.tsbuildinfo",
     "lint": "npm run prettier:check && npm run tslint",
     "lint:fix": "npm run tslint:fix && npm run prettier:fix",
     "prettier:cli": "lb-prettier \"**/*.ts\" \"**/*.js\"",

tsconfig.json

@@ -2,7 +2,8 @@
   "$schema": "http://json.schemastore.org/tsconfig",
   "extends": "@loopback/build/config/tsconfig.common.json",
   "compilerOptions": {
+    "composite": true,
     "rootDir": "src"
   },
-  "include": ["src"]
+  "include": ["src/**/*", "src/**/*.json"]
 }