[WIP] Stop using reflection to deserialize JSON

[pmaytak]

One of the possible solutions to #2343.

JSON.NET methods like JObject.SerializeObject, .DeserializeObject, .ToObject, .Value use reflection. Updates code to serialize/deserialize objects by calling methods that don't use reflection, like JObject[] array indexers.
(Also merges JsonUtils class into JsonHelpers.)

• Create ISerializable interface with Serialize/Deserialize methods and implement in classes that are dependent on OAuth2Client (MsalTokenResponse, InstanceDiscoveryResponse, InstanceDiscoveryMetadataEntry, AdfsWebFingerResponse, DeviceCodeResponse).
• Update unit tests to pass with new code.
• Write unit tests to compare that new serialization/deserialization is the same as old.
• Update other needed classes so that silent & device code flows work end-to-end (ClientInfo, LocalImdsResponse)
• Run perf tests for serializing with new and old code.

Perf test results
.NET Core 3.1.12 (CoreCLR 4.700.21.6504, CoreFX 4.700.21.6905), X86 RyuJIT

Method	Categories	Mean	Error	StdDev	Ratio
Serialize, MsalTokenResponse, With Reflection	Serialize, MsalTokenResponse	4.920 μs	0.0548 μs	0.0513 μs	1.00
Serialize, MsalTokenResponse, Without Reflection	Serialize, MsalTokenResponse	8.210 μs	0.0867 μs	0.0768 μs	1.67
Deserialize, MsalTokenResponse, With Reflection	Deserialize, MsalTokenResponse	9.363 μs	0.1209 μs	0.0944 μs	1.00
Deserialize, MsalTokenResponse, Without Reflection	Deserialize, MsalTokenResponse	10.654 μs	0.0851 μs	0.0710 μs	1.14
Serialize, InstanceDiscoveryResponse, With Reflection	Serialize, InstanceDiscoveryResponse	41.122 μs	0.4426 μs	0.3923 μs	1.00
Serialize, InstanceDiscoveryResponse, Without Reflection	Serialize, InstanceDiscoveryResponse	51.787 μs	0.9862 μs	1.0962 μs	1.25
Deserialize, InstanceDiscoveryResponse, With Reflection	Deserialize, InstanceDiscoveryResponse	70.212 μs	0.6181 μs	0.5782 μs	1.00
Deserialize, InstanceDiscoveryResponse, Without Reflection	Deserialize, InstanceDiscoveryResponse	65.974 μs	1.1809 μs	1.1046 μs	0.94
Serialize, OAuth2ResponseBase, With Reflection	Serialize, OAuth2ResponseBase	2.137 μs	0.0356 μs	0.0297 μs	1.00
Serialize, OAuth2ResponseBase, Without Reflection	Serialize, OAuth2ResponseBase	2.804 μs	0.0068 μs	0.0061 μs	1.31
Deserialize, OAuth2ResponseBase, With Reflection	Deserialize, OAuth2ResponseBase	3.861 μs	0.0767 μs	0.0753 μs	1.00
Deserialize, OAuth2ResponseBase, Without Reflection	Deserialize, OAuth2ResponseBase	3.847 μs	0.0285 μs	0.0267 μs	1.00

[bgavrilMS]

Looks good so far

[bgavrilMS]

Great stuff.

[pmaytak]

Went with #2428 as a solution as it's less invasive and more reliable.