Require native Git runtime and bundle full manpages

- Remove the app fallback path when native Git is unavailable and show a startup blocker instead
- Fix native level setup for staged file counting and cherry-pick parity
- Improve manpage loading/search and bundle full Git documentation assets
- Integrate Git cross-compilation into AndroidProjectTooling.sh and remove debug AAB support

app/src/main/assets/manpages/git-merge-index.txt

@@ -0,0 +1,83 @@
+git-merge-index(1)
+==================
+
+NAME
+----
+git-merge-index - Run a merge for files needing merging
+
+
+SYNOPSIS
+--------
+[verse]
+'git merge-index' [-o] [-q] <merge-program> (-a | ( [--] <file>...) )
+
+DESCRIPTION
+-----------
+This looks up the <file>(s) in the index and, if there are any merge
+entries, passes the SHA-1 hash for those files as arguments 1, 2, 3 (empty
+argument if no file), and <file> as argument 4.  File modes for the three
+files are passed as arguments 5, 6 and 7.
+
+OPTIONS
+-------
+\--::
+	Do not interpret any more arguments as options.
+
+-a::
+	Run merge against all files in the index that need merging.
+
+-o::
+	Instead of stopping at the first failed merge, do all of them
+	in one shot - continue with merging even when previous merges
+	returned errors, and only return the error code after all the
+	merges.
+
+-q::
+	Do not complain about a failed merge program (a merge program
+	failure usually indicates conflicts during the merge). This is for
+	porcelains which might want to emit custom messages.
+
+If 'git merge-index' is called with multiple <file>s (or -a) then it
+processes them in turn only stopping if merge returns a non-zero exit
+code.
+
+Typically this is run with a script calling Git's imitation of
+the 'merge' command from the RCS package.
+
+A sample script called 'git merge-one-file' is included in the
+distribution.
+
+ALERT ALERT ALERT! The Git "merge object order" is different from the
+RCS 'merge' program merge object order. In the above ordering, the
+original is first. But the argument order to the 3-way merge program
+'merge' is to have the original in the middle. Don't ask me why.
+
+Examples:
+
+----
+torvalds@ppc970:~/merge-test> git merge-index cat MM
+This is MM from the original tree.		# original
+This is modified MM in the branch A.		# merge1
+This is modified MM in the branch B.		# merge2
+This is modified MM in the branch B.		# current contents
+----
+
+or
+
+----
+torvalds@ppc970:~/merge-test> git merge-index cat AA MM
+cat: : No such file or directory
+This is added AA in the branch A.
+This is added AA in the branch B.
+This is added AA in the branch B.
+fatal: merge program failed
+----
+
+where the latter example shows how 'git merge-index' will stop trying to
+merge once anything has returned an error (i.e., `cat` returned an error
+for the AA file, because it didn't exist in the original, and thus
+'git merge-index' didn't even try to merge the MM thing).
+
+GIT
+---
+Part of the linkgit:git[1] suite