Correct default build options in dev docs

Developer builds now use, across all platforms,

• INTERNAL_2GEOM=ON to use the latest version of lib2geom
• BUILD_TYPE=Debug to check assertions
• -DCMAKE_EXPORT_COMPILE_COMMANDS=ON to help IDEs like VSCode
• -DCMAKE_INSTALL_PREFIX=${PWD}/install_dir to have a consistent install_dir for other parts of the documentation

VSCode instructions for Windows now use the standard build command.

The advanced instructions explain how to use ninja instead of ninja install to save time

Fixes #5897 (closed)

Note: I have not tested this. Reviewers need to decide if we need to test first or if we can merge anyway.