Preselect dropdown values in the New Project Wizard

[sharon-wang]

Intent

• More UI work for Epic: New Project Wizards for Beta #2110

This PR pre-selects a default value in the dropdowns, so the user can click through to create the project without having to select anything (as long as they're happy with the defaults!)

Before (dropdowns not preselected)

This PR (dropdowns preselected with reasonable defaults)

Demo Vid

• this is more up-to-date than the above screenshot...and has dropdown styling! ✨

newprojwiz_dropdown.mp4

Approach

• Store the user's environment setup type (new env or existing env) in the new project wizard state
• Store the user's environment type (Venv or Conda) in the new project wizard state
• If the user navigates to the previous step and then to the Python environment step, the selections are persisted
  • Conda interpreters don't yet get persisted because their runtime IDs are placeholders
• Updates the Conda dropdown items to return PythonInterpreterInfo as their values
• Creates DropdownEntry which creates a consistent dropdown entry style/layout in the wizard

QA Notes

• The Python Environment dropdown should be pre-selected to Venv for now (hardcoded default)
• The Python Interpreter should be pre-selected to:
  • If Venv is selected: the user's preferred Global version of python
  • If Conda is selected: currently, we have hardcoded python versions for conda, so there is no default.
  • If Existing Python is selected: the user's preferred version of python