fix(web-types): add support for VDataTable pattern slots

[piotrtomiak]

Add support for VDataTable header.<name> and item.<name> slots in web-types metadata for better Vuetify support in JetBrains IDEs..

Description

This fix properly describes item and header slots according to the newest supported web-types format.

Motivation and Context

It fixes issue https://youtrack.jetbrains.com/issue/WEB-55216/False-positive-Unrecognised-slot-name-warning-for-slots-with-dot-notation-in-Vuetify-components

How Has This Been Tested?

Tested manually in the latest WebStorm version.

Markup:

// Paste your FULL Playground.vue here

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[KaelWD]

Where did you find the documentation for this?

[piotrtomiak]

@KaelWD I am developing Web Types support for WebStorm. The support for patterns arrived some time ago in WebStorm (and other IDEs). The main documentation source now is the Web Types schema - https://github.com/JetBrains/web-types/blob/master/schema/web-types.json . I will be providing a comprehensive documentation at a later stage.

[KaelWD]

Ah I didn't realise you were with jetbrains, I'll take your word that this works then I guess :P

[piotrtomiak]

@KaelWD Thanks for merging this!