Non-breaking spaces in documentation are kept with codegen

**Describe the bug**
If there are any non-breaking spaces in GraphQL documentation (char code 160), they are left intact in the generated documentation. This is not a huge issue per se, but eslint does not like it and it's probably right.

**To Reproduce**
Steps to reproduce the behavior:

1. My GraphQL schema:

```graphql
"""
This is a test with a non breaking space.
"""
type Query {
user(id: ID!): User!
}

type User {
id: ID!
username: String!
email: String!
}
```

2. My GraphQL operations:

```graphql
query user {
user(id: 1) {
id
username
email
}
}
```

3. My `codegen.yml` config file:

```yml
schema: schema.graphql
documents: document.graphql
generates:
types.ts:
plugins:
- typescript
- typescript-operations
```

**Expected behavior**
Non-breaking spaces should be replaced with _normal_ spaces.

**Additional context**
I will be happy to create a PR to change the current behavior, but I am not sure about a couple of points.
First of all, is it conceptually correct to _change_ the documentation? Probably we can all agree that things like non-breaking changes should not be used inside documentation, but that's also true for many, many other things (i.e.: `U+202e`). Should we exceptionally handle and transform non breaking spaces?
The second point is related to semver: something like this should be considered breaking, minor or fix? Transforming documentation will not _strictly break_ any code, but on the other hand it exposes users to possibly unexpected changes. What do you think?