This commit fixes an issue where paths on Windows are case insensitive, for instance when setting the build folder its name would be converted to lowercase.
The culprit is our realpath() function, that was calling os.path.normcase() internally, since we are removing that call it makes sense to just remove the function entirely and call os.path.realpath() wherever necessary.
Closes https://github.com/espressif/esp-idf/issues/10282
Previously get_idf_build_env didn't include the default environment
(os.environ) in its output, so the environment only contained the
variables returned by "idf_tools.py export".
If PATH already contains all the right paths, "idf_tools.py export"
doesn't return the PATH variable.
Therefore the environment returned by get_idf_build_env was usually
incomplete. Fix by combining the output of "idf_tools.py export" with
os.environ.
