Create rule S7111: "part of" directives should be used with strings (use_string_in_part_of_directives) (#4361)

Co-authored-by: antonioaversa <antonioaversa@users.noreply.github.com>

rules/S7111/dart/metadata.json

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+{
+  "title": "\"part of\" directives should be used with strings",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "2min"
+  },
+  "tags": [
+    "convention"
+  ],
+  "defaultSeverity": "Minor",
+  "ruleSpecification": "RSPEC-7111",
+  "sqKey": "S7111",
+  "scope": "All",
+  "defaultQualityProfiles": ["Sonar way"],
+  "quickfix": "unknown",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "LOW"
+    },
+    "attribute": "CLEAR"
+  }
+}

rules/S7111/dart/rule.adoc

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+`part of` directives should be used with strings, rather than with `library` names.
+
+== Why is this an issue?
+
+Often Dart libraries are small enough to be entirely contained in a single file. 
+
+However, when the file becomes too large and it's not possible to split the library into smaller libraries (as adviced by the Dart team in the note https://dart.dev/guides/libraries/create-packages#organizing-a-package[here]), Dart defines a
+`part of` directive, which allows developers to split the library into multiple smaller chunks.
+
+When a library is split into multiple files, each part has to refer the library it belongs to, and it can do so with two similar but alternative syntaxes:
+
+* by name identifier: `part of my_library;`
+* by a URI string: `part of 'my_library.dart';`
+
+The second syntax is more precise and flexible, because it explicitely identifies the file that contains the main body of the library, whereas a reference by identifier needs to be resolved to a URI by the Dart compiler. 
+
+=== What is the potential impact?
+
+If the `part of` directive is used with a library name, the Dart compiler may resolve the library incorrectly, if multiple libraries with the same name but different paths exist in the package.
+
+== How to fix it
+
+Convert the name identifier into a string, append the `.dart` extension, and prepend the relative path.
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,dart,diff-id=1,diff-type=noncompliant]
+----
+part of my_library;
+----
+
+==== Compliant solution
+
+[source,dart,diff-id=1,diff-type=compliant]
+----
+part of '../my_library.dart';
+----
+
+== Resources
+
+=== Documentation
+
+* Dart Docs - https://dart.dev/tools/linter-rules/use_string_in_part_of_directives[Dart Linter rule - use_string_in_part_of_directives]
+* Dart Docs - https://dart.dev/guides/libraries/create-packages#organizing-a-package[Packages - Organizing a package]
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+The part-of directive uses a library name.
+
+=== Highlighting
+
+The entire `part of` directive statement, including the semicolon: e.g. `part of my_library;`.
+
+endif::env-github,rspecator-view[]

rules/S7111/metadata.json

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+{
+}