Update codeblock parsing rule

[Skalakid]

This PR updates the codeblock parsing rule so it:

1. Doesn't accept any text before the code block opening syntax
2. Require a new line after the code block opening syntax and before the closing syntax

We introduce this change to make parsing rules when typing markdown text inside the Live Markdown input more similar to the result that the user can see after sending the message in E/App. The above changes allow us to create a more intuitive and logical way to use code blocks when typing. Simplifying the parsing rules will also protect us from many complex and hard styling possibilities in the future.

This PR is part of code fence and inline code block refactor in the react-native-live-markdown library - PR

Fixed Issues

Expensify/App#39518

Tests

1. Verify if the following scenarios aren't parsed as code fences:

```codeblock```

```test\ntest```

test ```\ntest\n```

2. Verify if only the following messages are parsed as code fences:

```\ntest\n```

```\ntest\n```test

test\n```\ntest\n```test

test\n```\ntest\n```\ntest

QA

Verify new parsing rules as specified in the Test section

[jmusial]

LGTM

[jmusial]

NAB, or part of this issue, but IMO the tests would benefit from making

Test code fencing with ExpensiMark syntax outside

a describe and having test cases as test with separate descriptions

[Skalakid]

Yeah, I think it applies to all other markdown tests. They are heavily mixed, so reorganizing them into describe sections would be beneficial

[os-botify]

🚀 Published to npm in 2.0.144 🎉

[jjcoffee]

@Skalakid We have a version bump PR in App that includes this change. Is it safe to do now or should we wait until you've completed your project?

[Skalakid]

@jjcoffee Yeah, it should be safe to bump it inside E/App now. It will just change codeblock parsing rules :D