Fix dev script, test scripts; add jest config file (fixes #62)

[weedySeaDragon]

Fixes #62

1. Added a configuration file for jest. Added "testMatches" patterns to explicitly include directories jest should consider as valid directories for tests and ignore the dist directory:

testMatch: [
    "<rootDir>/codegen/**/*.test.ts",
    "<rootDir>/e2e/**/*.ts",
    "<rootDir>/src/**/*.test.ts",
    "!**/dist/**",
  ]

2. dev script in package.json now first compiles everything to make sure it's all up to date, then runs pkl-typescript/main with a simple pkl module from the examples:

3. test:e2e explicitly specifies the ./e2e directory so that any future jest tests that need to run in different directories can be added. (And to make it clear that the e2e tests are all in that directory.)

4. Added test:pkl and test:jest to be able to run all pkl tests and all jest tests separately. This made it easy to...

5. Simplified test: it now just needs to run test:pkl and test:jest

Questions:

1. Should the tests first compile everything to ensure it's all up to date? This is what I'm used to. This would mean that we need a script to just explicitly compile/generate everything.
   • I'm used to having the dev script only compile/generate/etc., things so they're up to date, and having a separate script to do a test run (i.e. "tsx pkl-gen-typescript/main.ts ./examples/basic-intro/config.pkl"