MCOL-4685: Eliminate some irrelevant settings (uncompressed data and extents per file).

This patch:
1. Removes the option to declare uncompressed columns (set columnstore_compression_type = 0).
2. Ignores [COMMENT '[compression=0] option at table or column level (no error messages, just disregard).
3. Removes the option to set more than 2 extents per file (ExtentsPreSegmentFile).
4. Updates rebuildEM tool to support up to 10 dictionary extent per dictionary segment file.
5. Adds check for `DBRootStorageType` for rebuildEM tool.
6. Renamed rebuildEM to mcsRebuildEM.

dbcon/mysql/ha_mcs_sysvars.cpp

@@ -21,7 +21,7 @@
 #include "ha_mcs_sysvars.h"
 
 const char* mcs_compression_type_names[] = {
-    "NO_COMPRESSION",
+    "UNUSED",
     "SNAPPY",
     NullS
 };