Organize versioning library (#3309)

Versioning library is a big mess of things all into one file, this makes
it hard to contribute. Did this originally because I was going to deal
with multiple madeRequired and madeOptional over time but that will be
done later but finished the cleanup anyway.

Split the versioning.ts into multiple separate logical files:
- `decorators.ts`: Contains all the versioning decorators and accessor
- `internal-projection-functions.ts`: Contains implementation of the
helper function used inside the versioning projection(not meant for
external use)
- `projection.ts`: Contains the projection building functions
- `versioning.ts`: Contains the various versioning computation
function(timeline, etc.)


This makes it clearer of what is supposed to be public apis vs internal,
waht is just mean for decorator, projection, etc.

.chronus/changes/versioning-library-cleanup-2024-4-9-22-35-15.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: internal
+packages:
+  - "@typespec/versioning"
+---
+
+Organize versioning library