merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/git-unpack-file.txt

@@ -0,0 +1,28 @@
+git-unpack-file(1)
+==================
+
+NAME
+----
+git-unpack-file - Creates a temporary file with a blob's contents
+
+
+
+SYNOPSIS
+--------
+[verse]
+'git unpack-file' <blob>
+
+DESCRIPTION
+-----------
+Creates a file holding the contents of the blob specified by sha1. It
+returns the name of the temporary file in the following format:
+	.merge_file_XXXXX
+
+OPTIONS
+-------
+<blob>::
+	Must be a blob id
+
+GIT
+---
+Part of the linkgit:git[1] suite