fix(tests): Make .mocharc.js CWD-independent (#7329)

Move tests/browser/test/.mocharc.js to tests/browser and use
__dirname to make the require directive work regardless of where
mocha is invoked from.

Simplify the browser:test script accordingly, taking advantage
also of the mocha default of running all tests in the test/
subdirectory.

package.json

@@ -51,7 +51,7 @@
     "start": "npm run build && concurrently -n tsc,server \"tsc --watch --preserveWatchOutput --outDir 'build/src' --declarationDir 'build/declarations'\" \"http-server ./ -s -o /tests/playground.html -c-1\"",
     "tsc": "gulp tsc",
     "test": "gulp test",
-    "test:browser": "npx mocha ./tests/browser/test --config ./tests/browser/test/.mocharc.js",
+    "test:browser": "cd tests/browser && npx mocha",
     "test:generators": "gulp testGenerators",
     "test:mocha:interactive": "http-server ./ -o /tests/mocha/index.html -c-1",
     "test:compile:advanced": "gulp buildAdvancedCompilationTest --debug",

tests/browser/.mocharc.js

@@ -2,5 +2,5 @@
 
 module.exports = {
   ui: 'tdd',
-  require: 'tests/browser/test/hooks.js',
+  require: __dirname + '/test/hooks.js',
 };