RFR: 8354090: Refactor import warning suppression in Check.java

[Archie Cobbs]

On Wed, 9 Apr 2025 01:20:50 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

> This is split off as a sub-task of [JDK-8224228](https://bugs.openjdk.org/browse/JDK-8224228), which seeks to add `@SuppressWarnings` support for lexical features.
> 
> In JDK 9 and later, there is a special exception to the normal rules for deprecation and preview warnings, which is that these warnings are automatically suppressed for import statements. This is because an import statement is just a lexical shortcut, not an actual use of the symbol.
> 
> The current code in `Check.java` implements this by manipulating the current `Lint` instance directly, but this operation is incompatible upcoming changes to deferred lint handling. Instead, there can be an explicit flag for "import warning suppression" in `Check.java` to handle this. This will also make the code a bit clearer.

Thanks for the review!

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PR Comment: https://git.openjdk.org/jdk/pull/24532#issuecomment-2794233673