Fix plugin directory resolution for plugin managers

Use resolve() to properly handle symbolic links when determining
the plugin installation directory. Add fallback to search in
&runtimepath if the licenses directory is not found in the
primary location.

This fixes issues when the plugin is installed via plugin managers
like vim-plug, packer.nvim, lazy.nvim, etc., where the plugin
directory may not be directly relative to the working directory.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

plugin/licenser.vim

@@ -86,9 +86,19 @@ function! s:GetCommentStyle(filetype) abort
 endfunction
 
 function! s:AddLicenseHeader(license) abort
-	let plugin_dir = fnamemodify(expand('<sfile>'), ':h:h')
+	let plugin_dir = fnamemodify(resolve(expand('<sfile>')), ':h:h')
 	let license_file = plugin_dir . '/licenses/' . a:license . '.txt'
 
+	if !filereadable(license_file)
+		for runtime_path in split(&runtimepath, ',')
+			let alt_license_file = runtime_path . '/licenses/' . a:license . '.txt'
+			if filereadable(alt_license_file)
+				let license_file = alt_license_file
+				break
+			endif
+		endfor
+	endif
+
 	if !filereadable(license_file)
 		echohl ErrorMsg
 		echo 'License file not found: ' . license_file
@@ -131,9 +141,19 @@ function! s:AddLicenseHeader(license) abort
 endfunction
 
 function! s:CompleteFiletype(A, L, P) abort
-	let plugin_dir = fnamemodify(expand('<sfile>'), ':h:h')
+	let plugin_dir = fnamemodify(resolve(expand('<sfile>')), ':h:h')
 	let licenses_dir = plugin_dir . '/licenses/'
 
+	if !isdirectory(licenses_dir)
+		for runtime_path in split(&runtimepath, ',')
+			let alt_licenses_dir = runtime_path . '/licenses/'
+			if isdirectory(alt_licenses_dir)
+				let licenses_dir = alt_licenses_dir
+				break
+			endif
+		endfor
+	endif
+
 	if !isdirectory(licenses_dir)
 		return []
 	endif