ECMA-426 DecodeSourceMapSources reads a content slot only while its index
is within sourcesContent, so a shorter array leaves trailing sources
without content and a longer array adds no sources. Local application
analysis and browser collection rejected any length mismatch and dropped
every original from the map.
The content helper now checks only entry types. Browser collection drops
its separate check because the leaf schema already validates every
supplied entry, and the raw records are still budgeted before parsing.
Fixes#2821