date and time does not properly parse as a variable

[nikku]

Describe the Bug

FEEL is context sensitive and as such shall allow users, though not encouraged, to override special names such as date and date and time.

This seems to not be properly supported by feelin at this stage (playground ref)

Steps to Reproduce

Cf. playground ref.

Expected Behavior

With the following context:

{
  "date and time": "DATE AND TIME",
  "date": "DATE"
}

Evaluating the following expression:

{
  foo: date and time,
  bar: date,
  date and time: 10,
  date: 100,
  sum: date and time + date
}

Shall yield the following result:

{
  "foo": "DATE AND TIME",
  "bar": "DATE",
  "date and time": 10,
  "date": 100,
  "sum": 110
}

Environment

• Host (Browser/Node version), if applicable: [e.g. MS Edge 18, Chrome 69, Node 10 LTS]
• OS: [e.g. Windows 7]
• Library version: [e.g. 2.0.0]

[nikku]

There is two aspects to this:

• date and time not properly parsing as a variable (Correct parsing of date and time as a variable name lezer-feel#31)
• built-ins overriding local variables (which should not be the case!) (Allow local built in overrides #63)