HBASE-27691 Prevent filters from seeing synthetic scan start cells

[noslowerdna]

HBASE-27691

What changes were proposed in this pull request?

This patch disables StoreScanner's initial lazy seek for filtered non-Get scans. Doing so prevents synthetic lazy-seek Cells from being exposed to server-side Filters and Comparators, while retaining lazy seeking for unfiltered Scans and Gets.

Why are the changes needed?

A region start boundary is not guaranteed to be a valid application row key. Passing its synthetic Cell to a RowFilter comparator violates the Filter contract that filterRowKey receives the first actual Cell of a row and can result in unexpected exceptions when Filter / Comparator code attempts to parse a seemingly truncated or otherwise malformed row key.

In our case that manifested like this:

Caused by: java.lang.RuntimeException: java.io.EOFException
	at com.package.MyComparator.compareTo(MyComparator.java:133)
	at org.apache.hadoop.hbase.PrivateCellUtil.compareRow(PrivateCellUtil.java:1240)
	at org.apache.hadoop.hbase.filter.CompareFilter.compareRow(CompareFilter.java:148)
	at org.apache.hadoop.hbase.filter.RowFilter.filterRowKey(RowFilter.java:90)
	at org.apache.hadoop.hbase.filter.FilterListWithOR.filterRowKey(FilterListWithOR.java:345)
	at org.apache.hadoop.hbase.filter.FilterList.filterRowKey(FilterList.java:152)
	at org.apache.hadoop.hbase.filter.FilterListWithAND.filterRowKey(FilterListWithAND.java:227)
	at org.apache.hadoop.hbase.filter.FilterList.filterRowKey(FilterList.java:152)
	at org.apache.hadoop.hbase.filter.FilterWrapper.filterRowKey(FilterWrapper.java:108)
	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.filterRowKey(HRegion.java:7545)
	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:7361)
	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:7153)
	at org.apache.hadoop.hbase.regionserver.RSRpcServices.scan(RSRpcServices.java:3330)
	...

This change reinstates the protection intended by HBASE-6562, using its later proposed (unmerged) eager initial seek patch.

How was this patch tested?

A ROWCOL Bloom regression test verifies that a Comparator sees only the persisted row, not a synthetic region-boundary Cell. Focused tests also cover each lazy-seek decision branch.

mvn -ntp -pl hbase-server -am \
  -Dtest=TestScanner \
  -Dsurefire.failIfNoSpecifiedTests=false \
  test