text-input: fix active instance tracking #4911

Job	Run time
format	7s
clippy-check	2m 13s
smithay-check-features	2m 49s
check-msrv	1m 17s
Documentation on Github Pages	1m 27s
check-minimal	1m 13s
anvil-check-features	2m 39s
smallvil-check	45s
smithay-tests	2m 32s
WLCS: Core tests	1m 23s
WLCS: Output tests	1m 10s
WLCS: Pointer input tests	1m 19s
WLCS: Bad Buffer Test	1m 20s
	20m 14s

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