chore: upgrade ESLint to v10 with flat config

Migrate from ESLint v8 with legacy .eslintrc.json to ESLint v10 with
flat config (eslint.config.mjs).

- Replace eslint v8 with v10, @typescript-eslint/parser and
  @typescript-eslint/eslint-plugin with the unified typescript-eslint
  package
- Convert .eslintrc.json to eslint.config.mjs using tseslint.config()
- Move .eslintignore entries into the flat config ignores property
- Remove --config flag from lint script (flat config is auto-detected)
- Fix lint errors caught by new rules (trailing commas in
  generate-docs.ts, useless assignment)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dhensby

.eslintignore

@@ -0,0 +1,23 @@
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+    {
+        ignores: ['lib/'],
+    },
+    eslint.configs.recommended,
+    tseslint.configs.recommended,
+    {
+        rules: {
+            'comma-dangle': ['error', 'always-multiline'],
+            'no-shadow': ['error'],
+            'semi': ['error', 'always'],
+        },
+    },
+    {
+        files: ['test/**/*'],
+        rules: {
+            '@typescript-eslint/no-explicit-any': 'off',
+        },
+    },
+);

.eslintrc.json

@@ -41,7 +41,7 @@ async function updateUsage(
     actionYamlPath = 'action.yml',
     readmePath = 'README.md',
     startToken = '<!-- start usage -->',
-    endToken = '<!-- end usage -->'
+    endToken = '<!-- end usage -->',
 ): Promise<void> {
     if (!actionReference) {
         throw new Error('Parameter actionReference must not be empty');
@@ -105,7 +105,7 @@ async function updateUsage(
             .replace(/ \n/g, '\n'); //  Squash space followed by newline
         while (description) {
             // Longer than width? Find a space to break apart
-            let segment: string = description;
+            let segment: string;
             if (description.length > width) {
                 segment = description.substr(0, width + 1);
                 while (!segment.endsWith(' ') && !segment.endsWith('\n') && segment) {
@@ -170,5 +170,5 @@ async function updateUsage(
 updateUsage(
     `tediousjs/setup-sqlserver@v${version.split('.')[0]}`,
     path.join(__dirname, '..', 'action.yml'),
-    path.join(__dirname, '..', 'README.md')
+    path.join(__dirname, '..', 'README.md'),
 );