Add FieldNameMatching decode option.

[benluddy]

Description

When decoding a CBOR map into a Go struct, FieldNameMatching controls how string
keys are matched to struct fields in the destination struct and allows users to
require case-sensitive matches. The default value of this option preserves the
existing behavior, which prefers case-sensitive matches but will fall back to a
case-insensitive match.

PR Was Proposed and Welcomed in Currently Open Issue

• This PR was proposed and welcomed by maintainer(s) in issue feature: Decode option to require case-sensitive field name matches #432
• Closes or Updates Issue feature: Decode option to require case-sensitive field name matches #432

Checklist (for code PR only, ignore for docs PR)

• Include unit tests that cover the new code
• Pass all unit tests
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• Certify the Developer's Certificate of Origin 1.1
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Certify the Developer's Certificate of Origin 1.1

• By marking this item as completed, I certify
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Developer Certificate of Origin
Version 1.1

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[fxamacker]

Nice! 👍 Thanks again for opening this PR!

Fuzzer is running with checks enabled for default and non-default settings. I'll let it run overnight.

fuzz: elapsed: 45m39s, execs: 61050856 (22464/sec), new interesting: 83 (total: 3492)
fuzz: elapsed: 45m42s, execs: 61133672 (27651/sec), new interesting: 83 (total: 3492)