port: Support iteration for object in ForEach action

[Danieladu]

Fixes #3769

Description

Make it possible for Microsoft.ForEach action to traverse its keys and values.

Changes

There is no change while the value of itemsProperty is array.
If the property value is Object, user could use the "index" property to get the current key, and use "value" value to get current value.
For example:
given such object for property dialog.item:

{
  "k1":"v1",
  "K2":"v2"
}

and the action:

{
    "$kind": "Microsoft.Foreach",
    "itemsProperty": "dialog.item",
    "actions": [
        {
            "$kind": "Microsoft.SendActivity",
            "activity": "index is: ${dialog.foreach.index}, and value is: ${dialog.foreach.value}"
        }
    ]
}

The result would be:
index is: k1 and value is v1 and index is: k2 and value is v2

two other object traverse comparison

1. built-in function indicesAndValues

indicesAndValues is same with the above logic.

2. foreach, where and select builtin functions

These three functions would convert the key into "key" property, and convert value into "value" property. And there is no index property.
For example:

foreach(dialog.item, u, concat(u.key, ':', u.value))

Get:

["k1:v1", "k2:v2"]

[coveralls]

Pull Request Test Coverage Report for Build 948519520

• 11 of 11 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.002%) to 85.407%

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Totals
Change from base Build 943670693:	-0.002%
Covered Lines:	19278
Relevant Lines:	21472

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💛 - Coveralls