typespec-java, eng, Remove the dependency on submodule of microsoft/typespec

### Clear and concise description of the problem

Remove the dependency on submodule of microsoft/typespec

We can let agent to brainstorm potential solutions.

One short term solution I thought of is to just move all the code here (let microsoft/typespec do the manual sync, as we seldom release the unbranded emitter).

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [x] Read the [docs](https://azure.github.io/typespec-azure/).
- [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.