Add Json Payload Functionality for User Agent Feature Extension

[samsharma2700]

Description

Part 2 of UserAgent work. Previous PR: #3451
(Note: This PR is identical to #3489 but due to recent MDS GH rule compliance had to create new branch to allow merges from main)

• Adding necessary classes for UserAgentInfo json payload.
• Implements the current spec guidelines for this FE(https://microsoft.sharepoint-df.com/:w:/t/sqldevx/ERIWTt0zlCxLroNHyaPlKYwBI_LNSff6iy_wXZ8xX6nctQ?e=iP8q75)
• The payload is defined by a DTO(Data Transfer Object) class and a UserAgentInfo that implements spec constraints(character limits, bytes limits and field dropping logic etc.)
• Part 3 will make the changes to write the payload as a part of login flow

Testing

Builds are running and added unit tests to verify changes.

[Copilot]

Pull Request Overview

This PR implements JSON payload functionality for the User Agent Feature Extension, adding the necessary classes and logic to generate constrained JSON payloads containing driver and environment information. The implementation follows specification guidelines for field prioritization, size limits, and truncation behavior.

• Adds UserAgentInfo class with payload generation, size adjustment, and field truncation logic
• Creates UserAgentInfoDto as a data transfer object for JSON serialization with proper field mapping
• Implements comprehensive unit tests covering payload constraints, field dropping, and serialization contracts

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
UserAgentInfoTests.cs	Comprehensive unit tests for payload validation, field truncation, size adjustment, and JSON contract verification
UserAgentInfoDto.cs	Data transfer object with JSON property mappings and nested OS information structure
UserAgentInfo.cs	Core implementation with payload generation, size constraints, OS detection, and field prioritization logic
Microsoft.Data.SqlClient.csproj (netfx)	Project file update to include new UserAgent classes
Microsoft.Data.SqlClient.csproj (netcore)	Project file update to include new UserAgent classes

[codecov]

Codecov Report

❌ Patch coverage is 64.64646% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.29%. Comparing base (cf2bdc7) to head (13090ce).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...icrosoft/Data/SqlClient/UserAgent/UserAgentInfo.cs	61.95%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3582      +/-   ##
==========================================
+ Coverage   63.19%   65.29%   +2.09%     
==========================================
  Files         274      276       +2     
  Lines       62478    62577      +99     
==========================================
+ Hits        39486    40861    +1375     
+ Misses      22992    21716    -1276     

Flag	Coverage Δ
addons	90.82% <ø> (ø)
netcore	66.74% <62.88%> (-0.03%)	⬇️
netfx	69.16% <68.96%> (+2.99%)	⬆️

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