Detect class constants referenced only in PhpDoc types

[janedbal]

Closes #391

Problem

A class constant referenced only inside a PhpDoc type — an int-range bound int<1, self::MAX>, a generic argument, a bare Foo::BAR constant type, etc. — was reported as shipmonk.deadConstant.

PHPStan eagerly collapses such types down to a literal (int<1, self::MAX> → int<1, 100>), discarding the "this bound came from self::MAX" link. The reference survives only in the raw PhpDoc type AST, which no collector traversed.

final class PaginationInput
{
    public const MAX_PAGE_SIZE = 100; // was falsely reported as unused

    /** @param int<1, self::MAX_PAGE_SIZE> $pageSize */
    public function __construct(public int $pageSize) {}
}

Fix

ConstantFetchCollector now, for any node carrying a docblock, walks the resolved PhpDoc block for ConstFetchNode occurrences across any type position and emits the matching ClassConstantUsage.

• The docblock is fetched via FileTypeMapper::getResolvedPhpDoc(), which is memoized — for the docblocks PHPStan already resolved during analysis this is a cache hit, not a re-parse.
• Class names are resolved through the NameScope (imports, namespace) with self/static/parent handled explicitly; owner/inheritance/enum-case resolution reuses the existing getDeclaringTypesWithConstant().
• Constant masks (self::SIZE_*) stay out of scope — that is the enum-migration case from Mark constants are used when referenced in PHPDoc with self::SIZE_* #223, deliberately unchanged.

Performance

The per-node scan is gated behind a cheap str_contains($docComment->getText(), '::') pre-filter, so docblocks that cannot hold a class-constant reference short-circuit before any PhpDoc resolution or AST traversal.