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

[weidongxu-microsoft]

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

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