fix: toolbar style change will be invalid when inputting more than 2 characters at a time

[crasowas]

Description

This is a regression caused by #1710. I believe there is a reason why pasted text should not use toggledStyle, but unfortunately, I couldn't find more details about it.

However, when I allowed pasted text to use toggledStyle to fix issue #1864, an assertion failure occurred when pasted text that contains line breaks. This might be the reason why pasted text should not use toggledStyle.

This PR fixes issue #1864 and processes pasted text line by line.

Related Issues

• Fix When inputting more than 2 characters at a time, the toolbar style change will be invalid. #1864
• Related fix bug #1696 - Allow insert/replace styled text from clipboard #1710

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the package version in pubspec.yaml files.
• All existing and new tests are passing.
• I have run the commands in ./scripts/before_push.sh and it all passed successfully

Breaking Change

Does your PR require developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[EchoEllet]

This is a regression caused by #1710

Thank you for pointing that out.

The goal of #1710 PR is to fix a bug that was caused by another PR sent by me. The feature I was implementing was improvement & and fixed another bug

it appears that both PRs inadvertently introduced new issues.