Port TypeScript #63026: Fix crash from circularly-reentrant getEffectsSignature

[Copilot]

Ports microsoft/TypeScript#63026

Function-like type-level nodes (call signatures, function types, etc.) need their own detached flow node via IsControlFlowContainer to prevent typeof queries within them from being narrowed by the containing container's flow graph. Without this, code like the following triggers infinite recursion through getEffectsSignature:

unionOfDifferentReturnType1(true);
const unionOfDifferentReturnType1: { (a: any): number; } | { (a: number): typeof Date; };

The Go binder already had IsControlFlowContainer on these nodes (unlike the TS side which had temporarily lost it), but was missing the seenThisKeyword save/restore/propagation logic that the TS fix introduced.

Changes

• New ContainerFlagsPropagatesThisKeyword flag (1 << 9) — marks containers that should propagate seenThisKeyword upward (arrow functions, method/call/construct signatures, function/constructor types)
• seenThisKeyword lifecycle in IsControlFlowContainer branch — save, reset before bindChildren, set ContainsThis after, and conditionally propagate via PropagatesThisKeyword
• Clear NodeFlagsContainsThis alongside reachability flags during incremental reset, matching TS behavior
• Updated GetContainerFlags to apply PropagatesThisKeyword to MethodSignature, CallSignature, FunctionType, ConstructSignature, ConstructorType, and ArrowFunction

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[jakebailey]

Nothing seems to change, confusingly

[jakebailey]

I think this needs #2748 to make sense, or rather, this may be a noop after.