Closes https://github.com/microsoft/vscode-python-internalbacklog/issues/290 closes https://github.com/microsoft/vscode-python-internalbacklog/issues/300

Key changes:

• We do all resolving in the environments resolver itself using resolverUtils.ts:
  • Factored out resolvers from low-level locators into a general resolver flat function.
  • Remove resolveEnv from ILocator interface.
• Ensure we only attempt to locate conda binary once per session whether it happens in resolver or locator.
• Change resolveEnv prototype to only accept a string.