Expand the managed API for Module, BasicBlock, Target, and instruction flags

[tannergooding]

Expands the high-level managed API (sources/LLVMSharp) to cover the
Phase-1 gaps that don't depend on new native libLLVMSharp helpers, moving
it closer to a faithful reproduction of the LLVM C++ API a real compiler or
JIT needs. Split into four logical commits by area.

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Module -- adds a context-scoped ownership registry to LLVMContext so a
Module is a cached, non-owning wrapper (consistent with the other managed
value/type wrappers), and fills out the full accessor set: identity, source
file name, target triple, data-layout string, module inline asm; function and
global lookup/insertion/enumeration; named struct-type lookup; and
print/verify/clone/bitcode. Also exposes ModuleIdentifier,
SourceFileName, and InlineAsm on LLVMModuleRef.

BasicBlock -- parent, terminator, first/last instruction, next/previous
block, instruction enumeration, and move/remove/erase helpers.

Instruction flags + derived accessors -- round-trips the poison-generating
and fast-math flags through the C API instead of native helpers:
HasNoSignedWrap/HasNoUnsignedWrap move onto LLVMGetNSW/GetNUW
with setters, and Exact, disjoint, non-negative, GEP no-wrap, in-bounds,
icmp same-sign, and fast-math flags are added -- each guarded by the owning
instruction kind so a release build never reads the wrong SubclassOptionalData
bits. Also adds the trivially-derived CalledFunction, GEP index/pointer
operands, and load/store pointer/value operands (no new interop).

Target / TargetMachine / DataLayout -- description, JIT/target-machine/
asm-backend queries, and target enumeration on Target; CPU, feature string,
target, and triple on TargetMachine; a target-data constructor plus
call-frame alignment, element offset, and element-containing-offset on
DataLayout. Adds the matching getters on LLVMTargetRef and
LLVMTargetMachineRef.

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Builds clean (0 warnings, TreatWarningsAsErrors) with 5 new managed tests;
full suite green. This is the managed half; the native libLLVMSharp helpers
and the managed accessors that consume them follow separately once the native
packages are rebuilt.