Remove redundant configuration from [DllImport] declaration

[terrajobst]

Immo proposal here: #33808 (comment)

Flag places where an attribute is set on a DllImport that's already the default value.

Category: Style

[jeffhandley]

Estimates:

• Analyzer: Small
• Fixer: Small

[carlossanlop]

@terrajobst can you please clarify what you meant in the description? What does it mean "an attribute is set on a DllImport"?

cc @AaronRobinsonMSFT since you linked #34831 and maybe you understand what the description means.

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[alexrp]

E.g. [DllImport(..., SetLastError = false)] or [DllImport(..., CharSet = CharSet.Ansi)] (etc) are pointless because those are already the default values.

[AaronRobinsonMSFT]

@carlossanlop the response from @alexrp is what I interpreted as the intent of this issue.