Add more context for validation errors for target properties.

[yyvch]

Add more context for validation errors for target properties.

Motivation:

I came across a post https://forums.swift.org/t/getting-error-on-package-resolve/75419 which reports the error message to be not clear. I thought I could clarify the message.

error: 'xerr': target 'Penny' contains a value for disallowed property 'settings'

Modifications:

I've updated the message for the error, so it includes more details to narrow down what is the culprit:

• highlight that the property depends on the target type
• show the value of the property, so that there's a hint what line in the Package.swift lead to the error (for example, linkerSettings or cxxSettings)

Result:

Before:

error: 'xerr': target 'Penny' contains a value for disallowed property 'settings'

After:

error: 'xerr': target 'Penny' is assigned a property 'settings' which is not accepted for
the binary target type. The current value of the property has the following representation: 
[PackageModel.TargetBuildSettingDescription.Setting(
tool: PackageModel.TargetBuildSettingDescription.Tool.linker,
kind: PackageModel.TargetBuildSettingDescription.Kind.linkedFramework("AVFoundation"),
condition: nil)].

[yyvch]

@swift-ci please test

[yyvch]

@swift-ci please test

[bkhouri]

@swift-ci test windows