GO-4162 corrupted links in markdown import

[AnastasiaShemyakinskaya]

https://linear.app/anytype/issue/GO-4162/corrupted-links-in-markdown-import

The problem is that we don't handle cases, when block have more than one markdown besides links. For example link can be also bold or italic.

To fix it

• I check if text block have more than one markdown
• Then I go through all marks in text block and change the type of mark to page mention in case it is link to existing page or file.

[github-actions[bot]]

Previous Coverage	48.4% of statements
New Coverage	48.5% of statements
Patch Coverage	67.3% of changed statements (37/55)

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^{Coverage provided by https://github.com/seriousben/go-patch-cover-action}