Support lsp_references for tags in frontmatter

[GordianDziwis]

The LSP_references functionality is not working as expected for tags defined in the YAML frontmatter of a document. While it correctly identifies and processes tags written inline as #tag, it fails to recognize tags listed in the frontmatter section.

Steps to Reproduce:

1. Create a new document with the following YAML frontmatter:

   ---
   aliases: Title
   tags:
     - tag
     - another_tag
   ---

2. Attempt to use LSP_references on the tags defined in the frontmatter.
3. Observe that LSP_references does not recognize or process these tags.

Expected Behavior:
LSP_references should identify and process tags defined in the YAML frontmatter, treating them the same way as inline tags (#tag).

Actual Behavior:
LSP_references ignores tags defined in the YAML frontmatter and only works with inline tags.

[artempyanykh]

Thanks for reporting this @GordianDziwis! YAML frontmatter support in marksman is very limited. It's a good feature to have though!