fit lsp-ui-imenu to longest line in buffer #501

Job	Run time
test (ubuntu-latest, 27.2, false)	1m 1s
test (ubuntu-latest, 28.2, false)	51s
test (ubuntu-latest, 29.3, false)	57s
test (macos-latest, 27.2, false)	4m 5s
test (macos-latest, 28.2, false)	4m 14s
test (macos-latest, 29.3, false)	4m 25s
test (windows-latest, 27.2, false)	1m 27s
test (windows-latest, 28.2, false)	1m 14s
test (windows-latest, 29.3, false)	1m 17s
test (ubuntu-latest, snapshot, true)	48s
test (macos-latest, snapshot, true)	4m 8s
test (windows-latest, snapshot, true)	47s
	25m 14s

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