docs: mark context.getPhysicalFilename() as deprecated

docs/src/extend/custom-rules.md

@@ -130,7 +130,7 @@ The `context` object has the following properties:
 * `parserServices`: (`object`) Contains parser-provided services for rules. The default parser does not provide any services. However, if a rule is intended to be used with a custom parser, it could use `parserServices` to access anything provided by that parser. (For example, a TypeScript parser could provide the ability to get the computed type of a given node.)
 * `parserOptions`: The parser options configured for this run (more details [here](../use/configure/language-options#specifying-parser-options)).
 
-Additionally, the `context` object has the following methods:
+Additionally, the `context` object has the following methods & properties:
 
 * `getAncestors()`: (**Deprecated:** Use `SourceCode#getAncestors(node)` instead.) Returns an array of the ancestors of the currently-traversed node, starting at the root of the AST and continuing through the direct parent of the current node. This array does not include the currently-traversed node itself.
 * `getCwd()`: Returns the `cwd` option passed to the [Linter](../integrate/nodejs-api#linter). It is a path to a directory that should be considered the current working directory.
@@ -145,7 +145,8 @@ Additionally, the `context` object has the following methods:
     * If the node is an `ImportSpecifier`, `ImportDefaultSpecifier`, or `ImportNamespaceSpecifier`, the declared variable is returned.
     * Otherwise, if the node does not declare any variables, an empty array is returned.
 * `getFilename()`: Returns the filename associated with the source.
-* `getPhysicalFilename()`: When linting a file, it returns the full path of the file on disk without any code block information. When linting text, it returns the value passed to `—stdin-filename` or `<text>` if not specified.
+* `getPhysicalFilename()`: (**Deprecated:** Use `context#physicalFilename` instead.) When linting a file, it returns the full path of the file on disk without any code block information. When linting text, it returns the value passed to `—stdin-filename` or `<text>` if not specified.
+* `physicalFilename`: When linting a file, it returns the full path of the file on disk without any code block information. When linting text, it returns the value passed to `—stdin-filename` or `<text>` if not specified.
 * `getScope()`: (**Deprecated:** Use `SourceCode#getScope(node)` instead.) Returns the [scope](./scope-manager-interface#scope-interface) of the currently-traversed node. This information can be used to track references to variables.
 * `getSourceCode()`: Returns a `SourceCode` object that you can use to work with the source that was passed to ESLint (see [Accessing the Source Code](#accessing-the-source-code)).
 * `markVariableAsUsed(name)`: (**Deprecated:** Use `SourceCode#markVariableAsUsed(name, node)` instead.)  Marks a variable with the given name in the current scope as used. This affects the [no-unused-vars](../rules/no-unused-vars) rule. Returns `true` if a variable with the given name was found and marked as used, otherwise `false`.