Try to slim down the dependencies of `gimli-symbolize`

This is a pretty small dependency for the `gimli-symbolize` feature, and
in an effort to reduce the number of external dependencies this commit
inlines the small amount of code we used from that crate here directly.
This should hopefully make this a bit easier to port to libstd
eventually.

* Remove coresymbolication implementation

This isn't used anywhere by default any more and I don't think there's
any reason to enable it. This older implementation uses private APIs
which aren't supposed to be used. Additionally libbacktrace nowadays
should be workable enough and with gimli soon on the horizon that should
be a suitable default for macOS and iOS.

* Disable android emulator in CI

* Remove dladdr fallback and implementation

This has been present for a very long time but I believe this has never
actually been that necessary. Non-MSVC platforms all use libbacktrace by
default, and libbacktrace will consult symbol tables of object files to
do what `dladdr` does, just inside of libbacktrace. Additionally gimli
implements the same logic. I believe that this means that `dladdr` isn't
necessary for resolving any symbols since our other strategies should
already be doing everything for us.

This commit makes the feature defunkt and otherwise removes the various
forms of fallback to dladdr.

* Switch to the `object` crate for object parsing

This commit switches the gimli feature from the `goblin` crate to the
`object` crate for parsing object files. The main motivation here is
trimming the dependencies of the `gimli-symbolize` feature to a bare
minimum. The `object` crate itself has no dependencies now and should be
a relatively easy drop-in replacement for the `goblin` crate.

* Parse fat libraries on macOS

This commit updates the object parsing code for macOS to support fat
libraries. This enables gimli to symbolize addresses coming from system
libraries which are currently installed frequently as fat libraries.

Closes #319

* Fix macOS symbolication of system libraries

This commit fixes an issue where symbolication of system libraries
didn't work on macOS. Symbolication through the symbol table was always
off by a slide amount for the library. It's not entirely clear why this
kept happening or what was going on, but some poking in LLDB's source
revealed a way we can differentiate and figure out what addresses need
to be looked up in the symbol table. Some more information is contained
in the comments of the commit itself.

Closes #318

Co-authored-by: Philip Craig <[email protected]>

Prunes out the `gimli-symbolize` dependency tree to just 3 crates!

* Split out gimli implementation into multiple files

Move object-file-parsing code into three separate files which can be
shared between different platforms.

* Remove Windows-specific block in avma_to_svma

* Move `kernel32` dependency to deprecated section

This hasn't been used in ages actually!

* Remove the `unix-backtrace` feature

AFAIK there's not actual use case for this. This was added ages ago when
backtrace functionality was first implemented but we've always preferred
libunwind as an unwinder since it's more accurate. No platform uses this
by default today, so this commit is removing the support and we can
re-add it pretty easily if necessary for a new platform.

* Make libunwind/dbghelp features defunkt

AFAIK there's no current users of this crate who are tweaking the
various methods of capturing a backtrace or symbolizing a backtrace. I
believe everyone's just largely using the default features. Additionally
it would be extremely hard to *not* use the default features given the
wide usage of this crate.

Given all this this commit simply removes the option of doing so.
Instead this crate will automatically select the best implementation
strategy per-platform and will provide the necessary support to enable
it. It's intended to that this should give a much better default
experience the avoids futzing around with features so much.

This commit updates `#[cfg]` and organization to ensure that the
gimli-symbolize feature compiles on all platforms. The main thing to
implement will be loading native libraries which currently doesn't have
an implementation for platforms like FreeBSD.

This commit switches this crate to using `gimli` by default for parsing
DWARF debug information. This is a long time coming and brings a number
of benefits:

* Primarily, Rust is safe. The libbacktrace library has been plagued
  with segfaults ever since we first started using it. Gimli, however,
  is almost entirely safe code. This should make us much more resilient
  in the face of buggy debuginfo.

* Secondarily, it means this library no longer needs a C compiler. Being
  an all-Rust crate generally makes it much easier to cross-compile,
  port, etc.

* Finally, this paves the road for future improvements such as
  split-debuginfo support by default. The libbacktrace library hasn't
  really changed since we started using it years ago, and this gives us
  more control over what's used and how now.

Closes #189