Reduce string allocations from the link tag

[ashmaroli]

• This is a 🔨 code refactoring.

Summary

Currently with the link tag, we have a string interpolation inside an iteration block:

jekyll/lib/jekyll/tags/link.rb

Lines 25 to 29 in 959fc18

	site.each_site_file do |item|
	return relative_url(item) if item.relative_path == relative_path
	# This takes care of the case for static files that have a leading /
	return relative_url(item) if item.relative_path == "/#{relative_path}"
	end

In a site with lots of files, the string interpolation on L#28 can result in a lot of unnecessary String allocations especially if the link tag is rendered in multiple pages.

The simplest solution is to stash the interpolated string in a variable outside the iterating block and reference it as necessary.

[ashmaroli]

@jekyllbot: merge +fix