Fix helpers not working in e2e tests

It errors that jest is not defined so put it behind a function instead
of immediately creating the mock (this is probably a better pattern
anyway).

The constant tests had to be reworked a little. Since the logger mock is
hoisted it runs before createLoggerMock is imported. I moved it into a
beforeAll which means the require call also needed to be moved
there (since we need to mock the logger before requiring the constants
or it'll pull the non-mocked logger).

This means getPackageJson needs to be a let and assigned afterward. To
avoid having to define a type for getPackageJson I just added a let var
set to the type of the imported constants file and modified the other
areas to use the same paradigm.

I also replaced some hardcoded strings with the mocked package.json
object.

test/utils/helpers.ts

@@ -2,16 +2,21 @@ import * as fs from "fs"
 import * as os from "os"
 import * as path from "path"
 
-export const loggerModule = {
-  field: jest.fn(),
-  level: 2,
-  logger: {
-    debug: jest.fn(),
-    error: jest.fn(),
-    info: jest.fn(),
-    trace: jest.fn(),
-    warn: jest.fn(),
-  },
+/**
+ * Return a mock of @coder/logger.
+ */
+export function createLoggerMock() {
+  return {
+    field: jest.fn(),
+    level: 2,
+    logger: {
+      debug: jest.fn(),
+      error: jest.fn(),
+      info: jest.fn(),
+      trace: jest.fn(),
+      warn: jest.fn(),
+    },
+  }
 }
 
 /**