Fix request body serialization issues caused by property tracking logic

[timayabi2020]

Summary
This PR removes the custom property tracking (TrackProperty, IsPropertySet) implementation introduced in the AutoRest-generated model classes to control request body serialization.

Root Cause
The tracker was originally added to support:

Explicit property tracking for selective serialization

Type inferencing improvements in ToJson()

Allowing users to explicitly set null on supported fields

However, this approach introduced significant instability in the cmdlet behavior — especially during first-time use within a PowerShell session. Specifically:

Properties that were set correctly (e.g. passwordProfile.password, displayName) were not serialized if they were not tracked in time

Nested model properties were dropped unless explicitly tracked and materialized before serialization

The timing of TrackProperty() invocation became unreliable due to dynamic type conversion and delayed binding in the PowerShell runtime

As a result, critical properties were inconsistently omitted from request payloads, leading to broken API calls and hard-to-reproduce bugs.

Fix
This change removes the TrackProperty and IsPropertySet directives and restores PowerShell’s default permissive behavior:

All explicitly set properties (including nested model fields) are now included in the serialized request body by default

Behavior is consistent across first-time and repeated cmdlet usage

The JSON output is no longer dependent on reflective timing or session state

Impact
Fixes multiple reported issues (#3286, #3298, #3304, #3307, #3308, #3309) with properties missing in request payloads

Aligns request body serialization with standard PowerShell model handling

No breaking change expected — only improves consistency