Improve 1.21.0 release note
Improve 1.21.0 release note

Change passive to active voice.
Add backticks around Java types and SQL keywords.
Fix release date.

looker-open-source/calcite,looker-open-source/calcite,googleinterns/calcite,vlsi/calcite,googleinterns/calcite,julianhyde/calcite,jcamachor/calcite,googleinterns/calcite,julianhyde/calcite,datametica/calcite,datametica/calcite,googleinterns/calcite,datametica/calcite,apache/calcite,looker-open-source/calcite,vlsi/calcite,vlsi/calcite,jcamachor/calcite,xhoong/incubator-calcite,datametica/calcite,julianhyde/calcite,vlsi/calcite,jcamachor/calcite,xhoong/incubator-calcite,apache/calcite,datametica/calcite,jcamachor/calcite,googleinterns/calcite,julianhyde/calcite,looker-open-source/calcite,vlsi/incubator-calcite,looker-open-source/calcite,datametica/calcite,xhoong/incubator-calcite,apache/calcite,apache/calcite,googleinterns/calcite,apache/calcite,julianhyde/calcite,julianhyde/calcite,vlsi/calcite,jcamachor/calcite,vlsi/incubator-calcite,xhoong/incubator-calcite,looker-open-source/calcite,jcamachor/calcite,apache/calcite,vlsi/calcite