fix(content): fix tab key handling of editor component with IME

[clomie]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

I often use tab key to composition string from the suggested clauses with IME, but using on editor.vue occurs unexpected behavior.
This PR is to avoid tab key handling on the editor.vue during text composition session.

Before	After

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

Testing event handling is a bit hard..., but l can try to add it so please let me know if it's needed.