avro

AVRO-2359: Support Logical Types in C# (#492)

* AVRO-2359: Support Logical Types in CSharp

* fix more warnings

* remove timezone change in TestTimestamp tests

* update logical Date and Time tests to be local time zone aware

* ensure TimeZone is set relative to a source TimeZone

* reparse Dates assuming local if they're not UTC

* try setting specific TimeZone offset

* actions for code review comments

* seperate the Timestamp* tests

* add missing license to AvroDecimalTests

* modify LogicalType to return .NET type rather than string

* add Register method to LogicalTypeFactory

* Fixup code-review comments

* Make Sign internal and add xmldocs

Co-authored-by: Fokko Driesprong <fokko@driesprong.frl>