Support the notion of a home directory separately from global configuration directory

 Define correct off64_t for AIX

#6422: handle dangling symbolic refs gracefully

Fixes issue #6156.

Signed-off-by: Sven Strickroth <email@cs-ware.de>

Fix build failure with -DEMBED_SSH_PATH

diff_file: Fix crash when freeing a patch representing an empty untracked file

Support OpenSSL 3 in dynamic loading mode

Add new PHP bindings project to language bindings section of README.md

Updates the README.md language binding section to reference a new
project providing PHP bindings at https://github.com/RogerGee/php-git2.

This prevents GIT_MMAP_VALIDATE from failing.
This also prevents git_diff_file_content__unload from attempting to free git_str__initstr.

Try to load OpenSSL 3 libraries when compiled with OpenSSL-Dynamic
support.

Handle the deprecated symbol renaming of SSL_get_peer_certificate to
SSL_get1_peer_certificate -- try to load the old name and if it fails,
use the new one.

When we fail to initialize the OpenSSL subsystem, don't assume that
we're "initialized". Subsequent initialization requests -- if there are
any -- should replay initialization and fail again.

We provide `BUILD_PATH` to our build script; provide it and mutate
`PATH` when running our tests as well.

We were previously using `cygpath` to try to convert a _list_ of Windows
paths into cygwin / Unix style `PATH` format. This does not work -- it
treats the path list as a single path (with semicolons -- understandably
as those are allowed characters in a Windows path).

For example, `C:\One;C:\Two;C:\Three` is converted to
`/c/one;c:/two;c:/three`.

Add a new function to convert path lists, so that paths are split by
semicolon and fed to `cygpath` independently, then re-joined with a
colon. This means that our example `C:\One;C:\Two;C:\Three` is correctly
converted to `/c/one:/c/two:/c/three`.

We provide `BUILD_PATH` to our build script; provide it and mutate
`PATH` when running our tests as well.

Teach the clone tests how to clone from github.com, when given a keypair
with a passphrase and known_hosts data. This allows us to better
exercise our known_hosts checking and ensure that the lifecycle of the
certificate callback matches our expectations.

libgit2 can now isolate its home directory, and our test runner (by
default) isolates the home directory. In our CI environment, we want to
set up some pieces (like ssh configuration) in a fake homedir. Continue
to do so and propagate that to clar.

Use a dummy home directory for tests to avoid user data leaking into
test execution.

Now that we've split the notion of the home directory from the global
configuration store, our tests should use the appropriate one based on
what they're doing.

Some callers -- like our test suite and the test suites of our language
bindings -- want to isolate the home directory to avoid accidentally
including the executing user's actual home directory data.

Previously, we combined the notion of a home directory and global
configuration -- now that this is separated, we provide users the
ability to configure both.

Users can specify a config file to be included in the home directory
using `~/filename` syntax. Instead of looking in the global
configuration location (which may be overridden), use the user's
_actual_ home directory. This allows callers to change the global
configuration location separately from the home directory.

Users can specify an attribute file to be included in the home
directory using `~/filename` syntax. Instead of looking in the
global configuration location (which may be overridden), use the
user's _actual_ home directory. This allows callers to change the
global configuration location separately from the home directory.

I spent an hour banging my head against this, when it was because the
remote didn't trust my key.

Use `git_sysdir_find_homedir_file` to identify the path to the home
directory's `.ssh/known_hosts`; this takes Windows paths into account by
preferring `HOME`, then falling back to `HOMEPATH` and `USERPROFILE`
directories.

Provide a mechanism to look up the user's home directory, using the same
mechanism that we use for locating the global configuration path (a
fancy name for saying "the home directory").

SSH known hosts lookups now use this, instead of simply looking at the
HOME environment variable, to support Windows-style home directory
lookups in `HOME`, `HOMEPATH`, or `USERPROFILE`.

The windows sysdir functions are libgit2-specific and for git
compatibility only; remove them from the shared util directory and bring
them into the libgit2 source tree.

Support OpenSSL3: add OpenSSL deprection warning compatibility flag

Add `OPENSSL_API_COMPAT=0x10100000L` since we use the now-deprecated
low-level hash functions.

ci: always create test summaries, even on failure

When the dependent jobs fail -- possibly due to test failures -- we
should still produce the job summary that shows those test failures.

tests: update clar test runner

Abstract time counter for tests; use gettimeofday on Unix and
GetTickCount on Windows.