Fix EnumMap lookups for enum constants with class bodies

[MoChiUaena]

EnumMap lookups fail when the first key is an enum constant with a class body. Its runtime class is a subclass of the enum, so passing getClass() to Enum.valueOf rejects valid keys.

Use getDeclaringClass() to resolve the key against the enum type. Add regression tests for dotted and bracketed paths, the lookup helper, missing and null values, empty maps, and unknown constant names.

Fixes #1083.

Validation:

• Full reactor: clean install -DskipTests, then clean package, on JDK 17 and 21. Each package run completed with 1,173 tests passed and 3 existing skips.
• Issue1083, Issue237 and Issue418: 11 tests passed on JDK 17. Before the fix, 6 of the 8 new cases failed with the reported exception.
• Spotless check passed for the two changed files. The unfiltered check reports formatting differences in six unchanged core files; the same files fail on the original base revision.