EGL Multifile BlobCache: Limit entry count

Limit the number of entries to 4096.

This is an empirical number based on app behavior. Some using many
small entries are taking a long time to load the cache.

Test: MultifileBlobCacheTest.CacheMaxEntrySucceeds
Bug: b/295051628
Bug: b/310535559
Change-Id: Ibc671cec25dd7c9bc10b9d1ee1fb837180eb7551