feat: add fallback parser

[antongolub]

This PR provides a support for custom JS/TS-based DSLs / templates which cannot be properly parsed with babel or tsc. In this case, depcheck turns into an unpassable syntax validator, but we still need a dependency checker.

• The new mode switch is controlled by a flag, and is disabled by default.
• Parser compatibility with tests is about ~99,45%.

Report

916 passing (2s)
  5 failing

  1) depcheck command line
       should output call stack for invalid files in JSON view:
     AssertionError: expected Object {} to have property '/depcheck/test/fake_modules/bad_js/index.js'
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.property (node_modules/should/cjs/should.js:356:19)
      at /depcheck/test/cli.js:151:12

  2) depcheck command line
       should not recognize JSX file when not pass jsx parser:
     AssertionError: expected Array [ 'No depcheck issue' ] to have property length of 2 (got 1)
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.length (node_modules/should/cjs/should.js:356:19)
      at /depcheck/test/cli.js:227:24

  3) depcheck command line
       should not recognize JSX file when not enable require detector:
     AssertionError: expected Array [ 'No depcheck issue' ] to have property length of 2 (got 1)
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.length (node_modules/should/cjs/should.js:356:19)
      at /depcheck/test/cli.js:241:24

  4) depcheck
       should ignore bad javascript:
     AssertionError: expected Array [] to have property length of 1 (got 0)
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.length (node_modules/should/cjs/should.js:356:19)
      at /depcheck/test/index.js:51:32

  5) depcheck
       should use custom detector to find dependencies:

      AssertionError: expected Array [ 'depend-1', 'depend-2', 'depend-3' ] to equal Array [] (at length, A has 3 and B has 0)
      + expected - actual

      -[
      -  "depend-1"
      -  "depend-2"
      -  "depend-3"
      -]
      +[]
      
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.deepEqual (node_modules/should/cjs/should.js:356:19)
      at /depcheck/test/index.js:176:34

[antongolub]

Hey, @rumpl,

Could you help me to move this forward?