feat: performance improvement for eventListeners

[JiaLiPassion]

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Since now DebugNode__PRE_R3__.triggerEventListener will use eventListeners method here

angular/packages/core/src/debug/debug_node.ts

Line 414 in f79110c

// We need to check whether `eventListeners` exists, because it's something

and it will use the method provided by zone.js, the current implementation is not performance efficient because it will loop all properties of the target and use regular expression to check the property name.

This PR will do better.

1. if the eventName parameter is not null (which is the most cases), we can directly get the event tasks from target.
2. if the eventName parameter is null, we will use the original logic.

[mhevery]

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