Convert symmetric crypto keys to use marker traits

[MGibson1]

traits and structs are markers for the purpose of the key

Type of change

- [ ] Bug fix
- [x] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Work on starting to make usage of crypto keys explicit at compile time

Code changes

• file.ext: Description of what was changed and why

Screenshots

Before you submit

• Please add unit tests where it makes sense to do so (encouraged but not required)

[bitwarden-bot]

Checkmarx One – Scan Summary & Details – 2fb9e101-bc01-4bfe-82d7-ddc451a47dd0

New Issues

Severity	Issue	Source File / Package	Checkmarx Insight
	Heap_Inspection	/languages/csharp/BitwardenSdk.cs: 34	Attack Vector
	Heap_Inspection	/languages/csharp/BitwardenSdk.cs: 27	Attack Vector

[Hinton]

After discussion with @MGibson1 we will continue using the new type pattern since it provides the benefit of not exposing the inner implementation. With the tradeoff of needing to duplicate traits on the newtype.