refactor: identifier escapes + "self" group (#339)

Co-authored-by: Ven <vendicated@riseup.net>

patches/eslint@8.28.0.patch

@@ -0,0 +1,45 @@
+diff --git a/lib/rules/no-useless-escape.js b/lib/rules/no-useless-escape.js
+index 2046a148a17fd1d5f3a4bbc9f45f7700259d11fa..f4898c6b57355a4fd72c43a9f32bf1a36a6ccf4a 100644
+--- a/lib/rules/no-useless-escape.js
++++ b/lib/rules/no-useless-escape.js
+@@ -97,12 +97,30 @@ module.exports = {
+             escapeBackslash: "Replace the `\\` with `\\\\` to include the actual backslash character."
+         },
+ 
+-        schema: []
++        schema: [{
++            type: "object",
++            properties: {
++                extra: {
++                    type: "string",
++                    default: ""
++                },
++                extraCharClass: {
++                    type: "string",
++                    default: ""
++                },
++            },
++            additionalProperties: false
++        }]
+     },
+ 
+     create(context) {
++        const options = context.options[0] || {};
++        const { extra, extraCharClass } = options || ''
+         const sourceCode = context.getSourceCode();
+ 
++        const NON_CHARCLASS_ESCAPES = union(REGEX_NON_CHARCLASS_ESCAPES, new Set(extra))
++        const CHARCLASS_ESCAPES = union(REGEX_GENERAL_ESCAPES, new Set(extraCharClass))
++
+         /**
+          * Reports a node
+          * @param {ASTNode} node The node to report
+@@ -238,7 +256,7 @@ module.exports = {
+                     .filter(charInfo => charInfo.escaped)
+ 
+                     // Filter out characters that are valid to escape, based on their position in the regular expression.
+-                    .filter(charInfo => !(charInfo.inCharClass ? REGEX_GENERAL_ESCAPES : REGEX_NON_CHARCLASS_ESCAPES).has(charInfo.text))
++                    .filter(charInfo => !(charInfo.inCharClass ? CHARCLASS_ESCAPES : NON_CHARCLASS_ESCAPES).has(charInfo.text))
+ 
+                     // Report all the remaining characters.
+                     .forEach(charInfo => report(node, charInfo.index, charInfo.text));