docs: clarify that FESM can depend on shared chunks

Closes angular#66569

Author: alan-agius4

adev/src/content/tools/libraries/angular-package-format.md

@@ -206,6 +206,7 @@ The Angular compiler can generate index ES module files. Tools like Rollup can u
 
 FESM is a file format created by flattening all ES Modules accessible from an entrypoint into a single ES Module.
 It's formed by following all imports from a package and copying that code into a single file while preserving all public ES exports and removing all private imports.
+However, in some cases, the FESM may depend on shared chunks that are shared between multiple entry points.
 
 The abbreviated name, FESM, pronounced _phe-som_, can be followed by a number such as FESM2020.
 The number refers to the language level of the JavaScript inside the module.
@@ -300,6 +301,7 @@ Short for ECMAScript Modules \(see above\).
 ### FESM
 
 Short for Flattened ES Modules and consists of a file format created by flattening all ES Modules accessible from an entry point into a single ES Module.
+Note that FESM is typically a single file, but it can depend on a shared chunk that is shared with other FESMs.
 
 ### Module ID