Add Crossgen2 symbol files to package

[AntonLapounov]

Add Crossgen2 symbol files to Crossgen2 NuGet symbol packages to make debugging easier. For instance, this PR adds the following symbol files to the Windows x64 package:

crossgen2.pdb
ILCompiler.DependencyAnalysisFramework.pdb
ILCompiler.Diagnostics.pdb
ILCompiler.ReadyToRun.pdb
ILCompiler.TypeSystem.ReadyToRun.pdb

clrjit_unix_arm_x64.pdb
clrjit_unix_arm64_x64.pdb
clrjit_unix_osx_arm64_x64.pdb
clrjit_unix_x64_x64.pdb
clrjit_win_arm_x64.pdb
clrjit_win_arm64_x64.pdb
clrjit_win_x64_x64.pdb
clrjit_win_x86_x64.pdb
jitinterface_x64.pdb

and the following symbol files to the Linux x64 package:

crossgen2.pdb
ILCompiler.DependencyAnalysisFramework.pdb
ILCompiler.Diagnostics.pdb
ILCompiler.ReadyToRun.pdb
ILCompiler.TypeSystem.ReadyToRun.pdb

libclrjit_unix_arm_x64.so.dbg
libclrjit_unix_arm64_x64.so.dbg
libclrjit_unix_osx_arm64_x64.so.dbg
libclrjit_unix_x64_x64.so.dbg
libclrjit_win_arm_x64.so.dbg
libclrjit_win_arm64_x64.so.dbg
libclrjit_win_x64_x64.so.dbg
libclrjit_win_x86_x64.so.dbg
libjitinterface_x64.so.dbg

Technically, packing clrjit_win_x64_x64.pdb for Windows x64 is not necessary since clrjit_win_x64_x64.dll points to clrjit.pdb; however, treating one of the JIT libraries specially is probably not worth extra complexity.

Fixes #57542. @dotnet/crossgen-contrib

[AntonLapounov]

/backport to release/6.0-rc1

[github-actions]

Started backporting to release/6.0-rc1: https://github.com/dotnet/runtime/actions/runs/1171134293