Rewrite and complete the Kaleidoscope tutorial samples (Ch3-8, ORC LLJIT)

[tannergooding]

The Kaleidoscope samples were built against the abandoned LLVMSharp 5.0.0 NuGet package (LLVM 5, 2017), not the in-repo library, so the API they called (LLVM.BuildCall, the legacy LLVMAdd*Pass function pass manager, MCJIT) was gone or reshaped in 21.x -- and the projects were OutputType=Library with a Main, so they didn''t even run.

Rather than patch the three dead chapters, this rewrites samples/KaleidoscopeTutorial on the in-repo LLVMSharp.Interop, ports the tutorial through Chapter 8, moves the JIT to ORC LLJIT, and restructures so the invariant frontend lives in a shared Kaleidoscope.Common library and each chapter contains only its delta over the previous one. Builds with 0 warnings (TreatWarningsAsErrors/Nullable on) and every chapter is smoke-tested end to end.

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Structure

• Kaleidoscope.Common -- lexer, token, full AST, base Parser + base CodeGenVisitor, the ORC LLJIT wrapper, the REPL loop, host functions, support helpers.
• Chapter3 emit IR (dump only); Chapter4 ORC LLJIT + new pass manager; Chapter5 if/for; Chapter6 user-defined operators; Chapter7 mutable variables (alloca + mem2reg); Chapter8 native object-file emission.

Each chapter''s Parser/CodeGenVisitor derive from the previous chapter''s and override only the new productions; Chapter{N} references Chapter{N-1}, so the incremental steps are visible instead of copied.

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What it fixes

• Example Kaleidoscope code does not work #248 -- the legacy function pass manager was retired upstream (LLVM 17); replaced with the new pass manager via LLVM.RunPasses(module, "function(mem2reg,instcombine,reassociate,gvn,simplifycfg)", tm, opts).
• Is it even possible to create a function call in the current codebase? #250 -- GetNamedFunction -> BuildCall2(GlobalGetValueType(fn), fn, args). The old code also sized the arg/param arrays with Math.Max(count, 1), so a zero-arg call passed a one-element array holding a null ref -- invalid IR and an access violation in VerifyFunction; now sized exactly.
• Update Kaleidoscope Chapters 3, 4 and 5 to use OrcJIT #1 -- moved to ORC LLJIT with a fresh module per top-level expression under its own resource tracker (added, looked up, removed), so a session of several expressions gives distinct results (foo(2,3)=25, foo(4,5)=81) instead of MCJIT re-running the first one''s code.
• Implementation of "extern" functions in Kaleidoscope #69 -- extern sin(x) resolves from the host C runtime via the ORC process-symbol generator; no mapping needed for libc symbols.
• Print and read input functions with LLVMSharp #133 -- putchard/printd injected as ORC absolute symbols backed by [UnmanagedCallersOnly] cdecl methods; printstar(5) prints *****.
• Add Kaleidoscope Chapters 6, 7 and 8 #2 / Please add the rest of the chapters in the tutorial #163 -- Chapters 6, 7, and 8 are delivered.

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Verified (Release): Ch4 foo(2,3)=25/foo(4,5)=81, extern sin resolves, 4+5 folds; Ch5 printstar(5) prints *****, if 1<2 then 10 else 20 -> 10; Ch6 !0=1/!1=0; Ch7 test(3)=8, iterative mutable fibi(10)=55; Ch8 emits a valid COFF x64 object exporting double average(double, double).

Out of scope: tutorial Chapter 9 (debug info / DWARF via DIBuilder) and Chapter 10. The samples are intentionally not part of the root LLVMSharp.slnx; a KaleidoscopeTutorial.slnx and a README.md describing the structure and chapter mapping are included.