8359493: Refactor how aggregated mandatory warnings are handled in the compiler

[archiecobbs]

The compiler's handling of the aggregation of mandatory warnings into "notes" at the end of compilation can be refactored to simplify the code.

The JCDiagnostic class supports flags that alter how warnings are handled, e.g., MANDATORY, NON_DEFERRABLE, etc. So instead of having to log aggregated mandatory warnings through a separate channel (the MandatoryWarningHandler), these warnings could instead be logged just like any other warning, but with an AGGREGATED flag added. The actual aggregation can then be handled "behind the scenes" by the logging subsystem.

This will also make it easier to implement @SuppressAnnotations support for parser/tokenizer warnings which require aggregated mandatory warning notes such as warnings for preview features.

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Issues

• JDK-8359493: Refactor how aggregated mandatory warnings are handled in the compiler (Sub-task - P4)
• JDK-8350514: Refactor MandatoryWarningHandler to support dynamic verbosity (Sub-task - P4)

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[archiecobbs]

/issue add JDK-8350514

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[openjdk]

@archiecobbs
Adding additional issue to issue list: 8350514: Refactor MandatoryWarningHandler to support dynamic verbosity.

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