[vscode] Some improvements for the CodeGeneration

[RodgeFu]

• 1. "select a language"'s list is empty when all emitters has been in tspconfig.yaml

• 2. the "Setting" Icon doesn't work (suggest to remove it which usually means goto vscode settings page)

• 3. Add an "all" option in the first step list

• 4. honor the default output dir from compiler by default: "emitter-output-dir: {output-dir}/{emitter-sub-folder}"

  https://typespec.io/docs/handbook/configuration/configuration/#configuring-output-directory

• 5. when user selects a new emitters, generate code directly instead of go back to the top list to ask user select again

• 6. remove the version check logic after the typespec library/emitters loose the dependency rule against compiler