[Migrated] Normalize compiler diagnostic messages

[rust-gpu-bot]

Issue automatically imported from old repo: EmbarkStudios/rust-gpu#565
Old labels: t: enhancement,a: error messages
Originally creatd by khyperia on 2021-03-31T11:15:30Z

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We're currently really inconsistent with our diagnostics style, e.g. some start with uppercase, some lowercase. We should change them to match rustc's style (casing, language style, etc.).

[rust-gpu-bot]

Comment from TuckerBMorgan on 2021-04-26T00:21:31Z

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Hey taking a look at this, looking at the rust source code, and style guides, is a specific document that you had in mind that you wanted followed?