Reduce allocations in DependencyHelper.GetExtensionRequirements

[kshyju]

Optimized the following methods to reduce memory allocations and improve deserialization performance:

1. DependencyHelper.GetExtensionRequirements()
2. RuntimeAssembliesInfo.GetRuntimeAssemblies()
3. RuntimeInformationProvider.BuildRuntimesGraph()

These methods previously used JObject.Parse to deserialize embedded JSON resources. This PR replaces them with System.Text.Json and source generation.

Before

Name	Total (Allocations)	Self (Allocations)	Total Size (Bytes)	Self Size (Bytes)
DependencyHelper.GetExtensionRequirements()	4,700	1	358,800	32
RuntimeAssembliesInfo.GetRuntimeAssemblies()	10,647	0	794,082	0

After

Name	Total (Allocations)	Self (Allocations)	Total Size (Bytes)	Self Size (Bytes)
DependencyHelper.GetExtensionRequirements()	420	12	31,548	384
RuntimeAssembliesInfo.GetRuntimeAssemblies()	1,432	0	101,568	0

Delta

• DependencyHelper.GetExtensionRequirements – Total allocations dropped by 4,280 (91.06%)
• DependencyHelper.GetExtensionRequirements – Total allocated size dropped by 319.5 KB (91.23%)
• RuntimeAssembliesInfo.GetRuntimeAssemblies – Total allocations dropped by 9,215 (86.56%)
• RuntimeAssembliesInfo.GetRuntimeAssemblies – Total allocated size dropped by 676.1 KB (87.21%)

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• [x ] I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information

[kshyju]

@fabiocav @soninaren Could you please review these changes since you both have historical context on this area?