Use more standard name for shared extension tsconfig

This enables Intellisense in the `tsconfig.base` file

extensions/php-language-features/tsconfig.json

@@ -1,9 +1,9 @@
 {
-	"extends": "../shared.tsconfig.json",
+	"extends": "../tsconfig.base.json",
 	"compilerOptions": {
 		"outDir": "./out"
 	},
 	"include": [
 		"src/**/*"
 	]
-}
+}