Do not override existing pyproject.toml keys during conversion

[rmartin16]

What is the problem or limitation you are having?

When an existing project is converted, keys should not be added to [tool.briefcase] when they already exist in [project]. For instance, if version is already specified in [project], do not add version = "0.0.1" to [tool.briefcase]. This should be considered for all PEP-621 pyproject.toml keys.

Describe the solution you'd like

Omit [tool.briefcase] keys from pyproject.toml that are already represented in [project].

Describe alternatives you've considered

Manually remove overriding keys from [tool.briefcase] post-conversion.

Additional context

No response

[freakboy3742]

Conceptually a good idea; but could be difficult to implement; the mechanism we're using to append pyproject.toml is (AFAIR) concatenation, rather than parsing and processing, so removing duplicate keys requires some pre-processing or a formatting-sensitive parser.

It may be better to consider this part of a broader migration to PEP621 format, so that a version field in [tool.briefcase] is no longer required or preferred.