feat(tsdefinition): short-name aliases + namespace mapping + linq.d.t…

[windischb]

…s auto-emission

v3.1.4 lands the "Monaco hovers show the short name instead of the 80-char namespace path" story, with one config that works for .d.ts AND NewObject:

• New IJsTsDefinitionContributor extension point; AddLinq auto-registers a contributor so linq.d.ts surfaces in GetTsDefinitions() output — closes the "linq.* is invisible in Monaco" gap from the FR
• AddTypeAlias() / MapNamespace(prefix, target) on JsEvalBuilder — aliases emit at root scope in the .d.ts AND resolve via NewObject(...); single source of truth lives on JsEngineOptions so the two layers cannot drift apart
• DefinitionBuilder.AddType(type, alias) / MapNamespace(source, target) for standalone (non-DI) consumers
• Collision detection fires only when a user rule is involved; natural same-name collisions (Span.Enumerator vs ReadOnlySpan.Enumerator) keep the v3.1.3 interface-merging behavior so unconfigured consumers don't regress
• System.* excluded from namespace mapping by default
• 8 new regression tests, 314/314 suite green

Pure additive release. No breaking changes to any existing API.