Ensure CaptureBinding.initializeBounds is called only once per binding

Fallout from https://github.com/eclipse-jdt/eclipse.jdt.core/pull/4862#issuecomment-3941063688:

> Inside `PTB.capture()` method `initializeBounds()` is invoked on only such elements `capturedArguments[i]` where `freshCaptures[i]` is true, which should "normally" imply that this capture binding has been created just now, i.e., never exposed to any outside code. [...]
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> Theory thus suggests, that the capture isn't really fresh, i.e., `this.environment.createCapturedWildcard()` probably answered a pre-existing capture binding. This smells like inference computing the same capture more than once, i.e., inference performing several attempts with similar inputs.
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> That theory also suggest, that it would be prudent to add an early exit to `CaptureBinding.initializeBounds()` to avoid repeated initialized in the first place (that would be an additional safety measure on top of the current fix).