Adds initial CI pipeline support

[dylon]

Major changes:

• Adds pipeline stages for running the unit tests on Ubuntu Linux, MacOS, and Windows.
• Adds pipeline stage for linting the sources.
• Cleans up existing sources according to the linter's recommendations.
• Replaces the test script for stubbing lfortran responses with sinon stubs for Windows compatibility (I could not get the script to run in the unit tests on Windows, and this is a better approach anyway).
• Updates dependencies since most of them were at least 2 years old.
• Adds CI pipeline status badges to README.

[certik]

The CI has the following failure in npm test:

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined
    at Object.writeFileSync (node:fs:2354:5)
    at LFortranCLIAccessor.runCompiler (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-accessors.ts:103:10)
    at LFortranCLIAccessor.showErrors (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-accessors.ts:241:33)
    at LFortranLanguageServer.validateTextDocument (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-language-server.ts:295:27)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5) {
  code: 'ERR_INVALID_ARG_TYPE'
}

But the test "passes". Is that expected?

---

How is LFortran installed at the CI? I can't find the installation process, but the tests seem to use it?

[dylon]

The CI has the following failure in npm test:

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined
    at Object.writeFileSync (node:fs:2354:5)
    at LFortranCLIAccessor.runCompiler (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-accessors.ts:103:10)
    at LFortranCLIAccessor.showErrors (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-accessors.ts:241:33)
    at LFortranLanguageServer.validateTextDocument (D:\a\lfortran-lsp\lfortran-lsp\server\src\lfortran-language-server.ts:295:27)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5) {
  code: 'ERR_INVALID_ARG_TYPE'
}

But the test "passes". Is that expected?

How is LFortran installed at the CI? I can't find the installation process, but the tests seem to use it?

The error is expected. The tests with errors check how well the server recovers from erroneous output from lfortran. mocha does not swallow stdout or stderr when it runs the tests, so all the logging information gets printed in the tests.

lfortran is not installed as part of the unit tests. I need to add an additional suite of integration tests for it and VSCode. The unit tests are intended to assert that our extension behaves as intended with the expected outputs from lfortran and the expected inputs from VSCode. The unit tests should not break if something changes in lfortran or VSCode, but the integration tests should. The integration tests will also be much slower to initialize and run.

Edit: I'll work on adding the integration tests for the rest of today. I didn't want this PR to get too big so I went ahead and submitted it.

Edit: The call to lfortran is stubbed with sinon in the unit tests. You'll see statements like sinon.stub(lfortran, "runCompiler").resolves(stdout). Those override the output from calling lfortran.runCompiler(...) to return whatever is the value of stdout. lfortran is not actually called from the unit tests.

[certik]

You can merge it. See #14 for adding lfortran.