Housekeeping: Fix equalOwnProperties

[s0]

equalOwnProperties() would incorrectly report two map-like objects as equal in the case where a property defined in left was not defined in right and whose value was considered "equal" to undefined by the equalityComparer.

This bug was found by an alert on LGTM.com

I've added unit tests that check around this functionality, which fail before the fix, and succeed after the fix commit.

Before 2c41d8b:

> jake runtests tests=compilerCore

...

Test failure:
correctly identifies undefined vs hasOwnProperty                [▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬․․․․․․․․․․․․․․․․․․․․․․․․․]
Test failure:
truthiness                                                      [▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬․․․․․․․․․․․․]
Test failure:
all equal                                                       [▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬]

  2 passing (2s)
  3 failing

  1) compilerCore
       equalOwnProperties
         correctly identifies undefined vs hasOwnProperty:
     Error: missing right property
      at Function.assert.isFalse (src/harness/harness.ts:10:78)
      at Context.<anonymous> (src/testRunner/unittests/compilerCore.ts:16:24)

  2) compilerCore
       equalOwnProperties
         truthiness:
     Error: missing right falsey property
      at Function.assert.isFalse (src/harness/harness.ts:10:78)
      at Context.<anonymous> (src/testRunner/unittests/compilerCore.ts:23:24)

  3) compilerCore
       equalOwnProperties
         all equal:
     Error: missing right property
      at Function.assert.isFalse (src/harness/harness.ts:10:78)
      at Context.<anonymous> (src/testRunner/unittests/compilerCore.ts:28:24)

After 2c41d8b:

> jake runtests tests=compilerCore

...

    compilerCore                                                [▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬]

  5 passing (245ms)

[msftclas]

All CLA requirements met.

[RyanCavanaugh]

Someone should write a static type checker for JavaScript 🤔

[RyanCavanaugh]

Thanks!