Analyzer: Validate literal arguments to StringSyntaxAttribute parameters/members

[stephentoub]

https://github.com/dotnet/runtime/pull/62995 added the new StringSyntaxAttribute, and we annotated a bunch of APIs with it, for the three syntaxes currently identified: Regex, DateTimeFormat, and Json.

Visual Studio will look for these and use it to influence its colorization, IntelliSense, etc., but we can also use them to help warn developers at dev time / build time when they've written something that will produce run-time failures. We can add an analyzer for each syntax that will warn on the literal provided, e.g. these would warn

var r = new Regex("[abc"); //  Invalid pattern '[abc' at offset 4. Unterminated [] set.
DateTime.ParseExact(DateTime.Now.ToString(), "c", null); // Invalid format specifier

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Issue Details

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https://github.com/dotnet/runtime/pull/62995 adds the new StringSyntaxAttribute and annotates a bunch of APIs with it, for the two syntaxes currently identified: Regex and DateTimeFormat. Visual Studio will look for these and use it to influence its colorization, IntelliSense, etc., but we can also use them to help warn developers at dev time / build time when they've written something that will produce run-time failures. We can add an analyzer for each syntax that will warn on the literal provided, e.g. these would warn ```C# var r = new Regex("[abc"); // Invalid pattern '[abc' at offset 4. Unterminated [] set. DateTime.ParseExact(DateTime.Now.ToString(), "c", null); // Invalid format specifier ```

Author:	stephentoub
Assignees:	-
Labels:	`area-System.Runtime`, `untriaged`, `code-analyzer`
Milestone:	-