Previously, `ngcc` assumed that if a format property was defined in
`package.json` it would point to a valid format-path (i.e. a file that
is an entry-point for a specific format). This is generally the case,
except if a format property is set to a non-string value (such as
`package.json`) - either directly in the `package.json` (which is unusual)
or in ngcc.config.js (which is a valid usecase, when one wants a
format property to be ignored by `ngcc`).
For example, the following config file would cause `ngcc` to throw:
```
module.exports = {
packages: {
'test-package': {
entryPoints: {
'.': {
override: {
fesm2015: undefined,
},
},
},
},
},
};
```
This commit fixes it by ensuring that only format properties whose value
is a string are considered by `ngcc`.
For reference, this regression was introduced in #32052.
Fixes#32188
PR Close#32205
f8b995dbf9