Infer arg types from new-object method chains and coalesce expressions

[TomasVotruba]

Problem

A parameter was narrowed to a single type when a sibling call site passed an argument the tool could not read.

$event->setTriggerRestrictedStartHour(new \DateTime()->modify('+2 hours'));
$event->setTriggerRestrictedStartHour('some');
$event->setTriggerRestrictedStartHour($element['triggerRestrictedStartHour'] ?? null);

The new \DateTime()->modify(...) chain and the ?? null coalesce contributed no type, so only 'some' was seen and the parameter became string - breaking the DateTime and null call sites.

Fix

• Resolve a method chain rooted at new X() to the receiver class X (fluent methods are assumed to return their receiver).
• Expand a coalesce argument A ?? B into the types of both sides, so ... ?? null keeps nullability.

The parameter above now resolves to the full union \DateTime|string|null.

Note

The receiver-type heuristic assumes a chained method returns its receiver. This is right for fluent/builder methods but wrong for one that returns something else (e.g. new \DateTime()->format(...) returns string, not DateTime). Flagging the trade-off explicitly.

Tests

Added collect cases for new-object chains (method and nullsafe) and coalesce arguments. Full suite, gofmt, vet, golangci-lint and modernize all pass.