Show resource name in taint -allow-missing warning

Context test updates

In some terminal emulators, writing a character into the last column on a
row causes the terminal to immediately wrap to the beginning of the next
line, even if the very next character in the stream is a hard newline.
That can then lead to errant blank lines in the final output which make
it harder to navigate the visual hierarchy.

As a compromise to avoid this, we'll format our horizontal rules and
paragraphs to one column less than the terminal width. That does mean that
our horizontal rules won't _quite_ cover the whole terminal width, but
it seems like a good compromise in order to get consistent behavior across
a wider variety of terminal implementations.

We were previously using some ASCII art to create some visual divisions
between parts of the diagnostic output. Now that we are requiring a UTF-8
terminal we can print out box drawing characters instead.

We now require the output to accept UTF-8 and we can determine how wide
the terminal (if any) is, so here we begin to make use of that for the
"terraform plan" command.

The horizontal rule is now made of box drawing characters instead of
hyphens and fills the whole terminal width.

The paragraphs of text in the output are now also wrapped to fill the
terminal width, instead of the hard-wrapping we did before.

This is just a start down the road of making better use of the terminal
capabilities. Lots of other commands could benefit from updates like these
too.

Here we propagate in the initialized terminal.Streams from package main,
and then onwards to backends running in CLI mode.

This also replaces our use of helper/wrappedstreams to determine whether
stdin is a terminal or a pipe. helper/wrappedstreams returns incorrect
file descriptors on Windows, causing StdinPiped to always return false on
that platform and thus causing one of the odd behaviors discussed in

Finally, this includes some wrappers around the ability to look up the
number of columns in the terminal in preparation for use elsewhere. These
wrappers deal with the fact that our unit tests typically won't populate
meta.Streams.

We need to call into terminal.Init in early startup to make sure that we
either have a suitable Terminal or that we disable attempts to use virtual
terminal escape sequences.

This commit gets the terminal initialized but doesn't do much with it
after that. Subsequent commits will make more use of this.

This is a helper package that creates a very thin abstraction over
terminal setup, with the main goal being to deal with all of the extra
setup we need to do in order to get a UTF-8-supporting virtual terminal
on a Windows system.

Remove any calls to testDiffFn and testApplyFn which don't effect the
test result. This way we have more tests using predictable provider
behavior, which is more likely to uncover legitimate regressions as the
particular behavior of the legacy mock provider logic does not need to
be taken into account.

Make errors in state mv more accurate

Fix error handling in instance apply methods

Now that we don't need to track separate error values for the apply
logic, it's easier to reorganize the diagnostic handling to use a single
set of diagnostics.

Trying to track these error values as they wint into and out of the
instance apply methods was quite difficult. They were mis-assigned, and
in many cases lost diagnostic information.

Show the resource name in the warning when allow-missing
is used and no resource matches

This was never assigned, and the empty value made the usage very
difficult to trace.

Various pieces of the state and/or warnings were dropped when the
provider returns an error. Do a little cleanup of `.apply` to make the
logic easier to follow.

Add documentation page for version

Remove revision from version command

preserve resource private data on error

If the provider returns an empty response during apply, we restore the
prior state for the resource, but the private data was not being
restored.

Update the MockProvider to use correct types and allow default behaviors

* docs: add links to the registry provider documentation

* Adjust wording/link URL
Co-authored-by: Nick Fagerlund <nick@hashicorp.com>

website: add example of multiple var cli

Add reasonable default behavior to the mock provider, so that may do not
need to depend on the idiosyncrasies of the old (though updated) test
testDiffFn and to a lesser extend the testApplyFn. This behavior is
based directly upon the documented resource lifecycle, rather
than be an ad-hoc collection of behaviors from old tests.

As a proof of concept, remove all uses of testDiffFn from the plan
context tests that don't cause the tests to fail.

The version command, although not the mightiest of our commands,
did not have a page among our docs.

The revision field is only populated on dev builds so this means
most releases of Terraform have an empty "terraform_revision" field
in the JSON output. Since we recommend developers use go tooling
to `go build` this tool when developing, the revision is not useful
data and so it is removed.

There are a few places where we want to perform some transformation on a
cty.Value, but require information from the schema. Rather than create
bespoke functions to walk the cty.Value and schema in concert, we can
provide Attribute information from a cty.Path allowing the use of
Value.Transform in these cases.

This ensures that test providers are using the same types as actual
providers.