Refactor/cleanup error handling code

[ilevkivskyi]

Various things in this PR:

• Minimized breakages of abstraction layers
• Added/updated docstrings/comments
• More consistent argument/attribute naming
• Removed redundant attributes/arguments (most important part probably)
• Fixed inconsistent order of arguments in helpers
• Added few asserts
• Removed some redundant normalizations w.r.t. defaults

This is 99% pure refactoring (that removes 100 lines of code), the only non-trivial (but still minor) things are:

• Fix end line/column for f-strings
• More consistent error formatting for some of the errors

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅