Add Xbox builders

[kaidokert]

Adds build configs to Xbox

b/266878119

[codecov]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (ebd0e67) 58.55% compared to head (6070faa) 58.56%.
Report is 34 commits behind head on main.

Files	Patch %	Lines
starboard/shared/posix/page_internal.cc	63.15%	7 Missing ⚠️
cobalt/dom/source_buffer_metrics.cc	0.00%	3 Missing ⚠️
starboard/elf_loader/program_table.cc	81.25%	3 Missing ⚠️
starboard/elf_loader/exported_symbols.cc	81.81%	2 Missing ⚠️
starboard/common/time.cc	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #1168    +/-   ##
========================================
  Coverage   58.55%   58.56%            
========================================
  Files        1914     1911     -3     
  Lines       94432    94585   +153     
========================================
+ Hits        55299    55390    +91     
- Misses      39133    39195    +62     

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[TyHolc]

Based on the build failures it looks like this might be missing either a UWP SDK or Xbox SDK

[kaidokert]

Based on the build failures it looks like this might be missing either a UWP SDK or Xbox SDK

Because it's still being executed in the wrong container - i put a todo / comment in the JSON file. I'd appreciate if someone can pick this up and land it - i won't make much forward progress in the next few days.