Markdown footnote validation

[mail2nnv]

Does this issue occur when all extensions are disabled?: Yes/No Yes

• VS Code Version: 1.73.1
• OS Version: Windows_NT x64 10.0.19044

Steps to Reproduce:

1. Create new markdown file
2. Type a text:

text[^1]
[^1]: footnote

3. See problems: (×) No link definition found: '^1' (link.no-such-reference) [Ln 1, Col 6]