doc: use 'object database' not ODB or abbreviation

The abbreviation 'ODB' is used in the technical documentation
sections for commit-graph and parallel-checkout, along with an
'odb' option in `git-pack-redundant`, without expansion.

Use 'object database' in full, in those entries. The text has not
been reflowed to keep the changes minimal.

While in the glossary for `object` terms, add the common`oid`
abbreviation to its entry.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

Documentation/git-pack-redundant.txt

@@ -34,7 +34,7 @@ OPTIONS
 
 --alt-odb::
 	Don't require objects present in packs from alternate object
-	directories to be present in local packs.
+	database (odb) directories to be present in local packs.
 
 --verbose::
 	Outputs some statistics to stderr. Has a small performance penalty.

Documentation/glossary-content.txt

@@ -262,7 +262,7 @@ This commit is referred to as a "merge commit", or sometimes just a
 	identified by its <<def_object_name,object name>>. The objects usually
 	live in `$GIT_DIR/objects/`.
 
-[[def_object_identifier]]object identifier::
+[[def_object_identifier]]object identifier (oid)::
 	Synonym for <<def_object_name,object name>>.
 
 [[def_object_name]]object name::

Documentation/technical/commit-graph.txt

@@ -17,7 +17,7 @@ There are two main costs here:
 
 The commit-graph file is a supplemental data structure that accelerates
 commit graph walks. If a user downgrades or disables the 'core.commitGraph'
-config setting, then the existing ODB is sufficient. The file is stored
+config setting, then the existing object database is sufficient. The file is stored
 as "commit-graph" either in the .git/objects/info directory or in the info
 directory of an alternate.
 

Documentation/technical/parallel-checkout.txt

@@ -56,7 +56,7 @@ Rejected Multi-Threaded Solution
 
 The most "straightforward" implementation would be to spread the set of
 to-be-updated cache entries across multiple threads. But due to the
-thread-unsafe functions in the ODB code, we would have to use locks to
+thread-unsafe functions in the object database code, we would have to use locks to
 coordinate the parallel operation. An early prototype of this solution
 showed that the multi-threaded checkout would bring performance
 improvements over the sequential code, but there was still too much lock