fix(managed): honor metadata ExtraData before table decoding (#1893)

Co-authored-by: LouisChen <3361008+chqcjq@users.noreply.github.com>
Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>

docs/managed-code-analysis.md

@@ -126,6 +126,13 @@ Member inspection binds build-local tokens, signatures, row offsets, method
 bodies, and decoded relationships to that artifact and MVID. Missing or malformed
 facts remain explicit in coverage and per-member status.
 
+Metadata table streams may carry the CLR-compatible `ExtraData` extension
+(`HeapSizes` flag `0x40`), which Microsoft readers honor although it is not
+specified by ECMA-335. REA skips its fixed four-byte word after the row counts
+before decoding table rows; the word's value is not a length. An incomplete
+word is reported as a metadata coverage failure at its file offset, without
+reading beyond the declared table stream.
+
 For unoptimized `#-` metadata, nonempty `FieldPtr` and `MethodPtr` tables
 translate TypeDef list positions to physical member definitions. REA resolves
 these indirections for member ownership and local attribute-constructor types;