refactor: break up god-methods and god-files (epic #1094)

[nickna]

Epic #1094 — break up god-methods and god-files

Pure mechanical extraction, no behaviour change. Interpreter and compiled output are
byte-identical; every change is a partial-class move or a semantics-preserving helper
extraction. Standalone compiled DLLs gain no SharpTS.dll dependency (no reflection
idioms were touched).

What changed, by sub-issue

#1142 — Extract realm/global state out of Interpreter.cs (3,065 → 1,978 lines)

• New Interpreter.Realm.cs: the process-wide globals table (CreateGlobalsLookup + the
  ordering-sensitive PromiseConstructorSentinel/_globalConstants/RegExpConstructorObject
  static trio, kept together and in textual order so static-init ordering is preserved),
  plus the per-realm Symbol.for registry, Math, primitive prototypes, RegExp.prototype,
  and globalThis routing helpers.
• The statement dispatch core and all Visit* handlers move next to their Execute* bodies
  in Interpreter.Statements.cs.

#1141 — Split the RuntimeEmitter mega-files

• RuntimeEmitter.CoreUtilities.cs (4,454 lines, four unrelated concerns) split into
  RuntimeEmitter.Coercion.cs (JS ToString/stringify, ToNumber/ToInt32, IsTruthy) and
  RuntimeEmitter.Operators.cs (relational, typeof, instanceof, in, +, ==, ===); the
  console-format block folded into the existing RuntimeEmitter.ConsoleHelpers.cs. All 32
  emitter methods relocated verbatim; CoreUtilities.cs removed.
• RuntimeEmitter.Objects.Properties.cs (5,222 → 3,090 lines): the whole Set* and Delete*
  emitter methods moved into RuntimeEmitter.Objects.SetProperty.cs and
  RuntimeEmitter.Objects.DeleteProperty.cs.
• Deferred: extracting the per-receiver branches inside the 2,028-line EmitGetProperty
  into helpers. That method emits IL through method-scoped labels/locals shared across every
  receiver branch; slicing it risks silent IL corruption that tests may not surface. Left as a
  follow-up — the file-level split above already removes the god-file smell.

#1143 — Right-size ObjectBuiltIns/BuiltInModuleTypes

• ObjectBuiltIns.cs (2,122 → 1,385 lines): the 21 Runtime* reflective property-descriptor
  helpers (invoked from compiled code) moved into ObjectBuiltIns.RuntimeDescriptors.cs,
  leaving the JS Object.* statics behind.
• BuiltInModuleTypes.cs (2,399 → 697 lines): per-module type signatures split into
  BuiltInModuleTypes.System.cs (fs/process/child_process/worker_threads/cluster/vm) and
  BuiltInModuleTypes.NetworkStreams.cs (dns/net/tls/http/dgram + stream); dispatch stays put.
• Deferred: converging the AST dispatch tables onto NodeRegistry/AstVisitorBase. The
  issue gates this on Epic 3 and describes it as "ideally source-generated" — a design change,
  not a mechanical move — so it is out of scope for this behaviour-preserving PR.

#1140 — Split the two type-checker god-methods

• CheckCall (~675 → ~295 lines): the entire builtin/special-case dispatch prologue extracted
  verbatim into TryCheckBuiltinCall(call, out result), preserving exact check order (zero
  reordering). CheckCall now delegates to it, then runs the general callable-resolution path.
• IsCompatibleCore: the clearly-delimited leading sections extracted into named
  TryRelate* helpers in the new TypeChecker.Compatibility.Relations.cs, mirroring the
  existing TryRelateDeferredMappedType pattern — TryRelateTypePredicate,
  TryRelateTypeParameters, TryRelateNeverUnknownObject, TryRelateNullUndefinedStrict,
  TryRelateLiteralTypes. Evaluation order is unchanged. The intricate, heavily-commented
  fall-through tail (iterator/generator/instance families) is deliberately left intact.

Validation

• dotnet test: 15404 / 0.
• SharpTS.Test262 (interpreter + compiled): baseline-green.
• SharpTS.TypeScriptConformance (type-checker): 31 / 0, no baseline regression.

Closes #1140
Closes #1141
Closes #1142
Closes #1143

Deferred scope filed as follow-ups under the epic: #1242 (EmitGetProperty
per-receiver branch extraction) and #1243 (AST dispatch-table convergence).

Part of #1094.