What kind of change does this PR introduce?

Bug fix.

What is the current behavior?

Minimap section headers (editor.minimap.showRegionSectionHeaders) are missing for //#region / //#endregion comments in jsonc files, even though vscode-json-languageservice already exposes folding ranges for those comments.

The reason is that minimap section headers are sourced from the language configuration's folding.markers, not from LSP folding ranges, and the json/jsonc language configuration does not declare folding markers.

Repro (in a .jsonc file, with editor.minimap.showRegionSectionHeaders enabled):

{
    "editor.showFoldingControls": "always",

    // MARK: Foo
    //#region Bar

    "editor.minimap.showRegionSectionHeaders": true

    //#endregion
}

Before this change: only the MARK: Foo header appears in the minimap.
After this change: both MARK: Foo and the Bar region label appear.

Fixes #219561

What is the new behavior?

Adds a folding.markers section to extensions/json/language-configuration.json matching the same patterns already used by vscode-json-languageservice for jsonc folding, and matching the convention used by typescript-basics, javascript, and other built-in language configurations:

"folding": {
    "markers": {
        "start": "^\s*//\s*#?region\b",
        "end": "^\s*//\s*#?endregion\b"
    }
}

The configuration is shared across json, jsonc, jsonl, and snippets. In practice these markers only match inside line comments (//...), which are syntactically valid only in jsonc and snippets; valid json/jsonl content cannot contain // outside of strings, so the markers are inert there. This matches the existing shared treatment of lineComment: "//" already declared in the same file.

How to test

1. Open Insiders with this change applied.
2. Create a .jsonc file with //#region NAME / //#endregion blocks.
3. Enable editor.minimap.showRegionSectionHeaders and confirm the region name appears in the minimap.
4. Confirm folding by the editor (Ctrl+Shift+[) still collapses the region as before.