[tcgc] clean up before stable

[tadelesh]

Tasks

Beta Give feedback

1. Consolidating some of the build in types: url vs uri, uuid vs guid
2. [Bug]: Typo in SdkDatetimeType #799
   bug lib:tcgc +2
3. The type of properties in SdkModelType should be SdkBodyModelPropertyType[] since we could never get an instance of other types inside the array #796
   lib:tcgc +1
4. encode in SdkBuiltinType should be optional or put sentinel values when an encoding is absent for the type #875
   lib:tcgc +1
5. SdkDurationType.writeType is too broad #26
   feature lib:tcgc +2
   
6. Could we specify the value type of SdkEnumType more precisely #876
   feature lib:tcgc +2
7. Revisit the type system in TCGC
8. Make Azure part extend from non-branding part of TCGC
9. values makes no sense in SdkUnionType #933
   lib:tcgc +1