Re-import data from ICU4C with starters in contraction-middle position marked in collation data

[hsivonen]

After unicode-org/icu#3411 has landed in ICU4C and before ICU4X 2.0, change datagen to import the icuexportdata zip file with that ICU4C PR having taken effect.

This does not require changes to the current ICU4X algorithms but will enable implementing #2712.

Once #2712 is implemented in ICU4X 2.x, ICU4X 2.x will no longer compute the right results with data that predates the above ICU4C PR. I'll leave it to folks who know ICU4X data policies better than me to decide if that means that we should increment the data version of CollationRootV1 and CollationTailoringV1 for ICU4X 2.0.