Internal ChangeFeed: Adds adoption of pagination library

[bchong95]

Internal ChangeFeed: Adds adoption of pagination library

Description

This PR adds the adoption of the new pagination library to ChangeFeed. This will enable us to have a single common code base for pagination across partitions, which has split proofing and the ability to simulate the service fabric emulator.

This is done by adding CrossPartitionChangeFeedAsyncEnumerator which implements IAsyncEnumerator<TryCatch<ChangeFeedPage>>. ChangeFeedIteratorCore now is just a wrapper around this class to provide API compact with FeedIterator internal.

While I was making this change I added a laundry list of improvements:

• Added ChangeFeedException, so that we have a base type that a visitor can convert to the proper CosmosException. This is in preparation for this enumerator to run in compute.
• Refactored the request option populators to take in a request option as input to avoid having to new one up per request.
• Added proper continuation token support for StartFromBeginning, StartFromTime, and StartFromNow.
• Switched over to CosmosElement for continuation token parsing and serialization
  ** This make the code exceptionless instead of throwing a newtonsoft exception
  ** Allows for continuation tokens to be composed
  ** Allows for continuation tokens to be serialized in binary
• ChangeFeed does not modify HasMoreResults on 304s.
  ** This avoids having to serialize to a continuation token and rehydrating the iterator everytime this happens.
  ** Also allows the user to write a customer retry handler on 304s and also implement client side long poll if they want
• Correctly aggregates the charge for 304 pages that we skipped for the user
• Buffers exceptions and returns an empty page with the aggregated stats
• Added ChangeFeed logic to InMemoryContainer so that we can unit test without the emulator.

The grammar for the cross partition change feed token is:

<composite_change_feed_token> : '[' <change_feed_token>, ... <change_feed_token> ']'
<change_feed_token> : '{' "FeedRange" ':' <feed_range>, "State" ':' <state> '}'
<feed_range> : '{' "type" ':' <feed_range_type>, "value" ':' <feed_range_value> '}'
<feed_range_type> : "Logical Partition Key" | "Physical Partition Key Range Id" | "Effective Partition Key Range"
<feed_range_value> : <logical_partition_key_json_string> | <physical_partition_key_id> | <epk_range>
<epk_range> : '{' "min": <string>, "max": <string>'}'
<state> : <start_from_begining_state> | <start_from_now_state> | <start_from_time_state> | <start_from_continuation_state>

An example token is:

[
    {
        "FeedRange":{
            "type":"Effective Partition Key Range",
            "value":{
                "min":"BF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF",
                "max":"DF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF"
            }
        },
        "State":{
            "type":"beginning"
        }
    },
    {
        "FeedRange":{
            "type":"Effective Partition Key Range",
            "value":{
                "min":"DF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF",
                "max":""
            }
        },
        "State":{
            "type":"continuation",
            "value":"88"
        }
    },
    {
        "FeedRange":{
            "type":"Effective Partition Key Range",
            "value":{
                "min":"7F-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF",
                "max":"9F-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF"
            }
        },
        "State":{
            "type":"now"
        }
    },
    {
        "FeedRange":{
            "type":"Effective Partition Key Range",
            "value":{
                "min":"3F-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF",
                "max":"5F-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF"
            }
        },
        "State":{
            "type":"time",
            "value":"2020-10-14T08:00:45.0937045Z"
        }
    }
]

Fixes #1918

[ealsur]

Blocking on three things:

1. The Emulator ContractTest change (see comment)
2. The new behavior is throwing exceptions on 304, we don't throw exceptions on Not Modified currently. Why do are we doing it now? The previous behavior would simply return an empty page and HasMoreResults would be false, so the loop ended. What is the reasoning to add exceptions now?
3. ChangeFeedOptions.EmitOldContinuationToken: What is the use case and what happens if the user leaves it enabled continuously?

[bchong95]

Blocking on three things:

1. The Emulator ContractTest change (see comment)
   responded to in comments.
2. The new behavior is throwing exceptions on 304, we don't throw exceptions on Not Modified currently. Why do are we doing it now? The previous behavior would simply return an empty page and HasMoreResults would be false, so the loop ended. What is the reasoning to add exceptions now?
   responded to in comments.
3. ChangeFeedOptions.EmitOldContinuationToken: What is the use case and what happens if the user leaves it enabled continuously?
   please read doc comments in source code.

[ealsur]

Synced offline. The migration test and format change to support previous customers was cleared up.

[ghost]

Closing due to in-activity, pease feel free to re-open.