- Fixes asserts and indentation
- Preserves additional tests and changes for repeatable and interfaces implementing interfaces.
- Doesn't add these two missing tests as they tests unsupported lagacy names:
  - it('maintains configuration of the original schema object'
  - it('adds to the configuration of the original schema object'

Tests no longer present in `graphql-js` has been moved to `SchemaExtenderLegacyTest`.
Respective commits that removed them from `extendSchema-test.js` are mentioned in comments.

Tests fail because:
- `repetable` in directives is lost when calling `extend()`
- `Schema::getAstNode()` returns `null` for an extended schema
- scalar types are added to schema automatically even if they are not used in SDL

Reasons, why tests fail (in addition to those mentioned in the previous commit):
- a problem with parsing/printing of types without fields (e.g. `type Query`)
- string comments become multiline (e.g. `"""Comment"""` becomes `"""\nComment\n"""`
- different order of definitions affects `printSchemaChanges()`
- missing `@` in directive name in error messages

…edBy)

…tive)

Resolves #1093

# Conflicts:
#	src/Utils/SchemaExtender.php

…eager-loading-schema

# Conflicts:
#	tests/Utils/SchemaExtenderTest.php

# Conflicts:
#	src/Utils/SchemaExtender.php
#	tests/Utils/SchemaExtenderTest.php

# Conflicts:
#	tests/Type/IntrospectionTest.php