feat: add experimental support for generics directive

[ota-meshi]

close #306
close sveltejs/eslint-plugin-svelte#521

generics are not yet marked as experimental features in this parser (Parsing of generics is not opt-in and is always enabled), but before official release, generics should be made experimental if they are still undocumented.

To use it you need to set parserOptions.svelteFeatures.experimentalGenerics to true.

[changeset-bot]

🦋 Changeset detected

Latest commit: 81e4201

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte-eslint-parser	Minor

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[coveralls]

Pull Request Test Coverage Report for Build 8127749354

Details

• 181 of 190 (95.26%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 91.604%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/context/script-let.ts	86	89	96.63%
src/context/fix-locations.ts	30	36	83.33%

Totals
Change from base Build 8094321933:	0.1%
Covered Lines:	2625
Relevant Lines:	2771

---

💛 - Coveralls

[coryvirok]

I eventually ended up here when searching for T is undefined error in my svelte 5 components when using generics="T". I'm hoping this comment gets indexed and others can find this more easily...

The fix is to update your eslint.config.js to include the option @ota-meshi mentioned.

E.g.

// eslint.config.js - generated by npx sv create app

import { fileURLToPath } from 'node:url'

import { includeIgnoreFile } from '@eslint/compat'
import js from '@eslint/js'
import prettier from 'eslint-config-prettier'
import svelte from 'eslint-plugin-svelte'
import globals from 'globals'
import ts from 'typescript-eslint'

const gitignorePath = fileURLToPath(new URL('./.gitignore', import.meta.url))

export default ts.config(
  includeIgnoreFile(gitignorePath),
  js.configs.recommended,
  ...ts.configs.recommended,
  ...svelte.configs['flat/recommended'],
  prettier,
  ...svelte.configs['flat/prettier'],
  {
    languageOptions: {
      globals: {
        ...globals.browser,
        ...globals.node,
      },
    },
  },
  {
    files: ['**/*.svelte'],

    languageOptions: {
      parserOptions: {
        parser: ts.parser,
        svelteFeatures: {
          experimentalGenerics: true,  // THIS FIXES THE TS ERROR
        },
      },
    },
  }
)