release: bump version to 2.0.0

[radoering]

Currently mainly a draft of the changelog.
The release will be done shortly before the Poetry 2.0 release.
The progress is tracked in python-poetry/poetry#9448.
(A few decisions are still to be made...)

Added

• Add support for the project section in the pyproject.toml file according to PEP 621 (#708, #792).
• Add support for non PEP440 compliant version in the platform_release marker (#722).
• Add support for string comparisons with in / not in in generic constraints (#722).
• Add support for script files that are generated by a build script (#710).
• Add support for SOURCE_DATE_EPOCH when building packages (#766, #781).

Changed

• Create METADATA files with version 2.3 instead of 2.2 (#707).
• Normalize source vcs URLs (#701).
• Make allow-prereleases a tri-state setting (#783).
• Rename exceptions to have an Error suffix (#767).
• Remove support for x in version constraints (#770).
• Remove support for scripts with extras (#708).
• Remove deprecated features and interfaces (#702, #769).
• Deprecate tool.poetry.dev-dependencies in favor of tool.poetry.group.dev.dependencies (#754).
• Deprecate Package.python_marker (#446).
• Improve Cygwin git support under Windows (#704).
• Improve error message when the pyproject.toml file cannot be parsed (#734).
• Improve handling of readme files (#752).
• Improve error handling when the Python constraint is empty (#761).
• Improve performance for creating a PEP 508 requirement from a dependency (#779).
• Update list of supported licenses (#706, #718, #727, #736, #746, #755, #764, #784, #787).

Fixed

• Fix an issue where the platlib directory of the wrong Python was used (#726).
• Fix handling of generic constraints (#732).
• Fix an issue where building a wheel in a nested output directory results in an error (#762).
• Fix an issue where + was not allowed in git URL paths (#765).
• Fix an issue where the temporary directory was not cleaned up on error (#775).
• Fix an issue where the regular expression for author names was too restrictive (#517).
• Fix an issue where basic auth http(s) credentials could not be parsed (#791).

Vendoring

TODO