fix: compare URI case insensitive

[powerman]

Neovim sends filenames to LSP as URI using lower case %-encoding. For some tools (when entry.Filename is not empty) current implementation converts filename to URI (using upper case %-encoding) and then compare two URI in case-sensitive way. This result in hard to notice issue: if filename contains non-ASCII symbols then some linters work (e.g. djlint) while others (e.g. markdownlint) doesn't work. And "doesn't work" here means Neovim gets no diagnostics even if there are some errors.