Added blue underline style to links in error messages to improve visibility in the error fallback component.

Change type

• improvement

Test plan

1. Trigger an error in the editor to show the DefaultErrorFallback.
2. Verify the "create a GitHub issue" link is blue and underlined.

• Unit tests
• End to end tests

Release notes

• Added styling for links in the error fallback component.

close #4927

<a href={url.toString()} style={{ color: 'blue', textDecoration: 'underline' }}>
	create a GitHub issue
</a>

Currently, tldraw seems to be styling with CSS. If it's good, I'll add a style for that function in css.
If so, more styles can be applied.
For ex...(There are concerns that writing this as style props may reduce readability.)

a {
  color: #0000ee; 
  text-decoration: underline; 
  cursor: pointer; 
}

a:visited {
  color: #551a8b; 
}

a:hover {
  color: #0000cc; 
  text-decoration: underline; 
}

a:active {
  color: #ff0000; 
}