Common Layers: [BREAKING CHANGE] renamed FdbTable to FdbMap and moved to namespace FoundationDB.Layers.Collections

- Tables have rows and columns, Maps avec keys and values
- Frees up the name "Table" for an actual layer about rows or column oriented tables.
- How to fix this breaking change: search/replace "FdbTable" to "FdbMap" and "FoundationDB.Layers.Tables" to "FoundationDB.Layers.Collections"
Async Linq: fixed missing "this" on AggregageAsync extensions methods, added ToDictionaryAsync() implementation
Fix typo in SliceComparer.Equals()
Cleaned up names in FdbMap unit test (table->map)