Share one NamespaceUses between the exported PHPDocs of a file

[ondrejmirtes]

Follow-up to #6583.

ExportedPhpDocNode held its own copy of the file's namespace, uses and constUses. The exportedNodes in the result cache therefore grew with the number of imports times the number of documented members. This is the same problem #6583 fixed in the file cache.

• ExportedPhpDocNode now refers to the NamespaceUses that NamespaceUsesTracker hands out. serialize() writes it once per result cache frame (one frame per file).
• A parallel worker sends exported nodes as JSON, which repeats the uses for every PHPDoc and loses the sharing. ParallelAnalyser now decodes each file's nodes with an ExportedNodeDecoder, which returns the same NamespaceUses instance for equal values. The decoder is passed explicitly through every decode() method, so there is no static state. The main process then holds a file's imports once, and the result cache it writes stays shared.
• The JSON shape is unchanged. ResultCacheManager::CACHE_VERSION is bumped because the serialized shape of ExportedPhpDocNode changed.

None of the ExportedNode classes are @api.

Numbers

Full self-analysis (parallel, result cache cleared), identical in two repeats:

	before	after
resultCache.php	54.9 MB	51.8 MB
peak RSS of the main process	461 MB	453 MB

The saving grows with imports × documented members, so the monolith in phpstan/phpstan#15304 should see a much larger difference.

Test

ExportedNodeResolverTest::testUsesAreStoredOncePerFile checks that the serialized exported nodes of a file contain each import once, both straight from the resolver and after a JSON round trip through decode(). The decoded nodes also have to be equals() to the originals. The test fails with 5 copies instead of 1 when either the resolver side or the decoder side stops sharing.

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