Add gitref macro to reference a git hash

With this extension a git hash can be easily referenced.

The porters handbook versions chapter uses this extension
as an example in the FreeBSD 14.0 version table.

An example of use

gitref:hash[repository="src|doc|ports",length=hash-longitude]

The repository should be src, doc or ports.
And if no length it's specified the macro will use 12 characters
of the specified hash.

PR:             253050
Submitted by:   jhb@

shared/lib/GitReferencesMacro/extension.rb

@@ -0,0 +1,25 @@
+require 'asciidoctor/extensions' unless RUBY_ENGINE == 'opal'
+
+include ::Asciidoctor
+
+class GitReferencesMacro < Asciidoctor::Extensions::InlineMacroProcessor
+  use_dsl
+
+  named :gitref
+
+  def process parent, target, attrs
+    hash = target
+    repository = if (repository = attrs['repository'])
+      "#{repository}"
+    else
+      "src"
+    end
+    length = if (length = attrs['length'])
+      length.to_i
+    else
+      12
+    end
+    url = %(https://cgit.freebsd.org/#{repository}/commit/?id=#{hash})
+    %(<a href="#{url}">#{hash[0, length]}</a>)
+  end
+end

shared/lib/git-macro.rb

@@ -0,0 +1,5 @@
+RUBY_ENGINE == 'opal' ? (require 'GitReferencesMacro/extension') : (require_relative 'GitReferencesMacro/extension')
+
+Asciidoctor::Extensions.register do
+    inline_macro GitReferencesMacro
+end