This commit adds generation of .ngsummary.js shims alongside .ngfactory.js
shims when generated files are enabled.
Generated .ngsummary shims contain a single, null export for every exported
class with decorators that exists in the original source files. Ivy code
does not depend on summaries, so these exist only as a placeholder to allow
them to be imported and their values passed to old APIs. This preserves
backwards compatibility.
Testing strategy: this commit adds a compiler test to verify the correct
shape and contents of the generated .ngsummary.js files.
PR Close#26495
31022cbecf