[4.0] Update Codemirror to v5.26.0

[C-Lodder]

Changelog

• In textarea-mode, don't reset the input field during composition.
• More careful restoration of selections in widgets, during editor redraw.
• vim bindings: Parse line offsets in line or range specs.
• javascript mode: More TypeScript parsing fixes.
• julia mode: Fix issue where the mode gets stuck.
• markdown mode: Understand cross-line links, parse all bracketed things as links.
• soy mode: Support single-quoted strings.
• go mode: Don't try to indent inside strings or comments.

[Fedik]

why to 4.x and not to 3.x, is there B/C issue?

[C-Lodder]

@Fedik - In 4.0 we use Grunt to manage vendor libraries. In 3.x it's a little different so it will need to be a separate PR. If I rightly remember, I think @brianteeman mentioned someone else normally managed the Codemirror updates for 3.x

[dgrammatiko]

@C-Lodder @Fedik the person in charge is @okonomiyaki3000
Also the code in Grunt in J4 was based on his repo for the code mirror!