[lexical-plaintext] Feature: add escape key handler

[jeffreyclu]

Description

Adds the same escape key handler to the plain text package as exists in lexical/richtext.

Closes: #5922

Test plan

Before

In the plaintext playground, pressing Esc doesn't blur the editor.

Screen.Recording.2024-04-30.at.11.02.59.AM.mov

After

In the plaintext playground, pressing Esc blurs the editor.

Screen.Recording.2024-04-30.at.11.02.32.AM.mov

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
lexical	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 30, 2024 2:57pm
lexical-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 30, 2024 2:57pm

[StyleT]

LGTM! Thanks for the contribution 🙌

[sqs]

(First, thank you for the Lexical editor. It's the best!)

Why is it desirable for Esc to blur the editor? That is not how most other text editors work. It makes sense for web browser location bars and modal text inputs, but not for multi-line document editor fields.

Here is an example of a situation where Esc blurring can be frustrating to the user:

1. Type @ and then realize you don't want to add an @-mention.
2. Press Esc a few times because usually Esc is idempotent.
3. Oops! Now you have not only exited the @-mention menu, but you've also blurred the editor and can't resume typing.

CleanShot.2024-05-26.at.14.55.40.mp4