[Feature] Add line break support for table cell

[MonoGray22]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

v7.15.5

Link to runnable example

https://milkdown.dev/playground?text=D4AgLgpgzmICYEMwJKAPAIwE4gPQD5URMcDUAoUALgFo766jaGmGaL1s9CRfPTC%2Fbh2JcyvIiWFCywcuSA%3D%3D

Steps to reproduce

1. Open page and navigate to the page/document containing the table.
2. Click on a table cell to put it in edit mode.
3. Type some content, then press Enter and observe whether a line break occurs.
4. Type more content, then press Shift+Enter and observe whether a line break occurs.

Expected behavior

Pressing Enter or Shift+Enter should break the line within the current cell, allowing multi-line input

Actual behavior

Neither Enter nor Shift+Enter triggers a line break within the cell, contradicting the expected behavior.

Runtime

No response

OS

No response

Build and bundle tools

No response

[Saul-Mirone]

It's not supported before. I will consider to support this in the future. And pr welcome.

[Saul-Mirone]

Syntax:

| Header 1 | Header 2 |
|---|---|
| This is the first line<br>This is the second line | Another cell |
| Item A | Item B<br>with a break |

Header 1	Header 2
This is the first line This is the second line	Another cell
Item A	Item B with a break