hl.fragsizeIsMinimum default ought to be 'true' for performance

hl.fragsizeIsMinimum was added in 8.5 with a default setting of false – thus producing average length fragments of fragsize instead of minimum beyond fragsize. In previous releases, even though the setting didn't exist, it was in-effect true (minimum). Unfortunately, this flip was found to be a significant performance regression for highlighting lots of text (especially when using the SENTENCE break iterator), and furthermore it seems to be of relatively minor value in fragment sizing.

I propose we flip this back to true.

https://lists.apache.org/thread.html/r2e44d290eac9edfa61ed9eced0d9f01a7bd1cbdf910344b2aa2368b8%40%3Csolr-user.lucene.apache.org%3E