Make target-pack ILAsm builds deterministic in BuildIlFile

[Copilot]

src/targetPacks/Directory.Build.targets assembled .il files without deterministic mode, producing non-reproducible PE timestamps/MVIDs for targeting-pack reference assemblies and causing downstream reproducibility drift. This update enables deterministic ILAsm output at the source.

• Build target update

  • Updated BuildIlFile in src/targetPacks/Directory.Build.targets to pass -deterministic to ilasm.

• Reproducibility impact

  • Ensures assemblies produced from target-pack .il sources are deterministic.
  • Eliminates a root source of nondeterminism that propagates into consumers compiling against these reference assemblies.

<Exec Command="$(IlasmPath) $(IlFile) -dll -quiet -nologo -deterministic &quot;-output=$(OutputFile)&quot;"
      IgnoreStandardErrorWarningFormat="true"
      CustomErrorRegularExpression=": error : " />

[omajid]

I tested this locally myself. It does wonders. For me, the html-diff-render (without any exclusions/filtering) is down from 4.36 MB to 376KB. A 91% reduction.