[Tree-widget]: fix scroll not persisting on widget change

[MartynasStrazdas]

closes iTwin/presentation#1097

fixes this issue for tree-widget v3

[github-actions]

Tree-Widget benchmark

Benchmark suite	Current: c643fa1	Previous: 5ca518d	Deviation	Status
categories tree creates initial filtered view for 50k items	4088.34 ms	4024.65 ms	1.58%	〰️
categories tree creates initial filtered view for 50k items (P95 of main thread blocks)	3345 ms	3325 ms	0.60%	〰️
categories tree changing category visibility changes visibility for 50k subCategories	4068.4 ms	4193.4 ms	-2.98%	〰️
categories tree changing category visibility changes visibility for 50k subCategories (P95 of main thread blocks)	3196 ms	3330 ms	-4.02%	〰️
categories tree changing definition container visibility changes visibility for 50k categories	6706.73 ms	6646.73 ms	0.90%	〰️
categories tree changing definition container visibility changes visibility for 50k categories (P95 of main thread blocks)	3993 ms	3836 ms	4.09%	〰️
models tree creates initial filtered view for 50k target items	965.47 ms	994.51 ms	-2.92%	〰️
models tree creates initial filtered view for 50k target items (P95 of main thread blocks)	90 ms	104 ms	-13.46%	〰️
models tree validates categories visibility for imodel with 50k categories	20959.95 ms	21027.83 ms	-0.32%	〰️
models tree validates categories visibility for imodel with 50k categories (P95 of main thread blocks)	6941 ms	6655 ms	4.30%	〰️
models tree changing model visibility changes visibility for 50k elements	2680.86 ms	2713.62 ms	-1.21%	〰️
models tree changing model visibility changes visibility for 50k elements (P95 of main thread blocks)	89 ms	127 ms	-29.92%	〰️
models tree changing category visibility changes visibility for 50k elements	3089.12 ms	2764.93 ms	11.73%	🚨
models tree changing category visibility changes visibility for 50k elements (P95 of main thread blocks)	80 ms	113 ms	-29.20%	〰️
models tree changing per-model-category override changes visibility for 50k elements	2831.08 ms	2934.03 ms	-3.51%	〰️
models tree changing per-model-category override changes visibility for 50k elements (P95 of main thread blocks)	21 ms	85 ms	-75.29%	✅
models tree changing element visibility changes only parent nodes visibility with 50k elements	3766.89 ms	3240.69 ms	16.24%	🚨
models tree changing element visibility changes only parent nodes visibility with 50k elements (P95 of main thread blocks)	331 ms	421 ms	-21.38%	✅

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