fix: rm BOM from file content on read

[everdro1d]

Problem statement

If a json file has utf-8 encoding, vim.json.decode will fail due to the BOM at the start. If package.json or snippet files are utf-8 encoded, it will fail to load. Resolves #52.

Proposed solution

This change removes the BOM from the file contents before attempting to decode.

function M.readAndParseJson(path)
-- ...
    -- See #52, #53. utf-8 encoded files have a BOM at the start which
	-- makes vim.json.decode fail. This removes the BOM if it exists.
    content = string.gsub(content, "^\xEF\xBB\xBF", "")
-- ...
end

AI usage disclosure

None used.

[chrisgrieser]

Could you add some explanation and/or reference the issue number in the comment? Just so it's clear for future work why that line is necessary.

Otherwise good to merge

[chrisgrieser]

Thanks for the PR!