fix(GlSearchBoxByType): Fix double input event

What does this MR do?

fix(GlSearchBoxByType): Fix double input event

Prior to this change, GlSearchBoxByType maintained its own local copy of the model value, which had a setter that emitted an input event when it changed. In addition, it forwarded all listeners to the underlying GlFormInput, which emits its own input event as well.

These two facts together meant that when a consumer explicitly added a listener (either via @input or v-model), it would be called twice: once by the computed setter's input event, and again by the GlFormInput's input event.

This change removes the unnecessary local copy of the model, and explicitly forwards the input event from the underlying GlFormInput.

Addresses #937 (closed).

Does this MR meet the acceptance criteria?

Conformity

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Addresses #937 (closed)