[7.x] Fix ComponentAttributeBag merge behaviour

[mfullbrook]

This PR is to fix the bug I raised in #31898. Below is an illustration of what this PR fixes.

With a component that defines some default attributes:

<table {{ $attributes->merge(['width' => '600', 'class' => 'mb-4']) }}>
  ...
</table>

If the component is used like this

<x-my-table width="100%" class="mt-2" />

We would expect the rendered template to be:

<table class="mb-4 mt-2" width="100%">
  ...
</table>

But the current implementation renders:

<table class="mb-4 mt-2" width="600">>
  ...
</table>

This PR fixes the implementation of ComponentAttributeBag::merge() so that it doesn't ignore attribute values specified in the template that is calling the component.

ViewComponentAttributeBagTest has been updated.