There was no test ensuring that we validate `.git` paths.  We do, but
let's add a test to make sure that we never regress this.

Introduce `git_path_validate_filesystem` which validates (absolute) on-disk
paths and `git_path_validate_workdir` to perform validations on (absolute)
working directory paths.  These functions are useful as there may be system
limitations on on-disk paths, particularly on Windows (for example,
enforcing MAX_PATH).

For working directory paths, these limitations may be per-repository, based
on the `core.longpaths` configuration setting.

If we want to validate more and different types of paths, the name
`git_path_validate` makes that easier and more expressive.  We can add,
for example, `git_path_validate_foo` while the current name makes that
less ergonomic.

Introduce a function to determine the number of Unicode characters in a
given UTF-8 string.

Move the utf8 functions into a proper namespace `git_utf8` instead of
being in the namespaceless `git__` function group.  Update them to
have out-params first and use `char *` instead of `uint8_t *` to match
our API treating strings as `char *` (even if they truly contain `uchar`s
inside).

tree: deprecate `git_treebuilder_write_with_buffer`

winhttp: skip certificate check if unable to send request

[skip ci]

commit-graph: Introduce `git_commit_graph_needs_refresh()`

commit-graph: Support lookups of entries in a commit-graph

The function `git_treebuilder_write_with_buffer` is unnecessary; it
is used internally as part of treebuilder writing, but it has little
use to external callers.  For callers that repeatedly write a
treebuilder, we can supply them with a buffer in the treebuilder struct
instead of recreating it.  For ourselves, when we want a single buffer
in our write loop, we can use an internal function.

merge: Check insert_head_ids error in create_virtual_base

Check git_signature_dup failure

insert_head_ids can fail due to allocation error

git_signature_dup can have an allocation failure

In some circumstances (e.g. when proxies are involved), winhttp will fail to reach the WINHTTP_CALLBACK_STATUS_SENDING_REQUEST phase. If this occurs, we'll error with ERROR_WINHTTP_INCORRECT_HANDLE_STATE when attempting to query the server certificate context (see https://docs.microsoft.com/en-us/windows/win32/api/winhttp/nf-winhttp-winhttpsendrequest#remarks).

To avoid this, verify that WinHttpSendRequest has reached the WINHTTP_CALLBACK_STATUS_SENDING_REQUEST phase before checking the certificate. Since we're using WinHTTP in synchronous mode, we know for sure that once WinHttpSendRequest returns we've either sent it successfully or not.

NOTE: WINHTTP_CALLBACK_STATUS_SENDING_REQUEST appears to be deprecated with no direct replacement. WINHTTP_CALLBACK_STATUS_SENDREQUEST_COMPLETE is only available in async mode, and there doesn't appear to be a method of querying this flag outside of the status callback.

Fix some typos

include: fix typos in comments

Fix documentation formating on repository.h

The enum 'git_repository_init_flag_t', 'git_repository_init_mode_t' and
the structure 'git_repository_init_options' does not follow the format
used by docurium.

index: Check git_vector_dup error in write_entries

This is for extra safety within write_entries

If allocating case_sorted.contents fails, git_vector_sort will segfault.

To prevent a race condition, these wlock/rlock calls should probably be checked
for errors.

Invert the workflow conditionals so that a workflow_dispatch event acts
like an on: push build.

Add new bindings for the R language

Update .gitignore

patch: add owner accessor

commit-graph: Introduce a parser for commit-graph files

revspec: rename git_revparse_mode_t to git_revspec_t

mwindow: Fix a bug in the LRU window finding code

The information about the type of a revision spec is not information
about the parser.  Name it accordingly, so that `git_revparse_mode_t`
is now `git_revspec_t`.  Deprecate the old name.

Only exclude tags files/folders and build folders at the repository root.