Add space for vertical stroke on message edit composer on Rich Text Editor mode

[luixxiul]

Fixes element-hq/element-web#25237

This PR intends to add space for vertical stroke on message edit composer of Rich Text Editor. It also suggests to add E2E tests for edit composers on both CIDER and RTE, with two new Percy screenshots: EditComposer on EventTile - CIDER and EditComposer on EventTile - Rich Text Editor.

Here are cropped screenshots of message edit composer on RTE mode:

Before	After

Please note that this PR intentionally suggests to create two EditComposer categories for CIDER and RTE, so that they will be added with other tests for each mode.

type: defect

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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Here's what your changelog entry will look like:

🐛 Bug Fixes

• Add space for vertical stroke on message edit composer on Rich Text Editor mode (#10749). Fixes The green left stroke on the event tile being edited is hidden with the Rich Text message editor on IRC layout  element-hq/element-web#25237. Contributed by @luixxiul.