Remove Spaceless Blocks from Twig Form Templates

In favor of using Twig's whitespace control operators. See #11277

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11277
| License       | MIT
| Doc PR        | 

Per @fabpot and @stof's requests in #11278, this is a PR for the 2.3 branch.