gitk: encode arguments correctly with "open"

While "exec" uses a normal arguments list which is applied as
command + arguments (and redirections, etc), "open" uses a single
argument which is this command+arguments, where the command and
arguments are a list inside this one argument to "open".

Commit bb5cb23 (gitk: prevent overly long command lines 2023-05-08)
changed several values from individual arguments in that list (hashes
and file names), to a single value which is fed to git via redirection
to its stdin using "open" [1].

However, it didn't ensure correctly that this aggregate value in this
string is interpreted as a single element in this command+args list.

It did just enough so that newlines (which is how these elements are
concatenated) don't split this single list element.

A followup commit at the same patchset: 7dd272e (gitk: escape file
paths before piping to git log 2023-05-08) added a bit more, by
escaping backslahes and spaces at the file names, so that at least
it doesn't break when such file names get used there.

But these are not enough. At the very least tab is missing, and more,
and trying to manually escape every possible thing which can affect
how this string is interpreted in a list is a sub-par approach.

The solution is simply to tell tcl "this is a single list element".
which we can do by aggregating this value completely normally (hashes
and files separated by newlines), and then do [list $value].

So this is what this commit does, for all 3 places where bb5cb23
changed individual elements into an aggregate value.

[1]
That was not a fully accurate description. The accurate version
is that this string originally included two lists: hashes and files.
When used with "open" these lists correctly become the individual
elements of these lists, even if they contain spaces etc, so the
arguments which were used at this "git" commands were correct.

Commit bb5cb23 couldn't use these two lists as-is, because it needed
to process the individual elements in them (one element per line of
the aggregate value), and the issue is that ensuring this aggregate
is indeed interpreted as a single list element was sub-par.

Note: all the (double) quotes before/after the modification are not
required and with zero effect, even for \n. But this commit preserves
the original quoting form intentionally. It can be cleaned up later.

Signed-off-by: Avi Halachmi (:avih) <avihpit@yahoo.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Taylor Blau <me@ttaylorr.com>