Refactor Wasmtime CLI to support components

[alexcrichton]

This commit refactors the wasmtime CLI executable to be able to
support not only compiling components but additionally executing
components. While I was doing this I've additionally added a new
--preview2 argument to enable using the new experimental
implementation of preview1 based on preview2 type/structs. This is
off-by-default but is expected to become the default in the future.

Some notable features of this change are:

• The preview1-implemented-with-preview2 module now sports
  add_to_linker_{async,sync} to replace the previous add_to_linker
  which always did async.

• Some trait bounds in the preview1-implemented-with-preview2 module are
  simplified.

• Some minor changes were made to wiggle's macros to support a "block
  on" that isn't the default wiggle dummy executor (as now we actually
  do need Tokio)

• Many options related to core wasm Linker configuration, such as
  --default-values-unknown-imports, are not implemented for components
  at this time. When used with components these options return an error.

• Construction of WASI contexts has been refactored to pass around fewer
  arguments to avoid threading through lots of values for both preview1
  and preview2.

• Reading the input to the Wasmtime CLI has been updated to read the
  input in the run subcommand before handing it off to the wasmtime
  crate's API to enable the CLI to use the contents of what's loaded to
  determine what to do next.

• Our generic ./ci/run-tests.sh script has been updated to pass the
  --features component-model flag to ensure that this CLI support is
  tested during the normal test suite.

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Procedural Note: this PR is based on #6833 and #6823 so the first few commits can be ignored.

[pchickey]

Various conflicts with main, and I'd like to leave the flush stuff out, but otherwise the meat of this is great.

[alexcrichton]

Ok I've ignored the one test that relies on output flushing and otherwise rebased this on main. I've additionally added component support for the wasi-nn feature by adding it to the component linker when a component is loaded on the CLI. I've left wasi-http as not-enabled, however, since I'm not familiar enough with what its current status is.

I think this should be ready to go though if you can give it another review @pchickey

[pchickey]

wasi-http is hosed at the moment and should not be enabled. @elliottt will hook it back in once its in a better state.