cmk-ui-library: cap the non-floating dropdown list height

On browsers with CSS anchor positioning, a long non-floating
CmkDropdown list grew to its full content height with no scrollbar and
covered the search input (e.g. the OpenTelemetry Azure ruleset metric
dropdown).

CMK-37626 replaced the fixed height cap with anchor positioning, but
the list stayed unbounded whenever a transformed ancestor became the
fixed containing block. Cap it to the viewport again so long lists
scroll.

CMK-38164

Change-Id: I214671adef10d04f9077477fb34e56425dc7d283