feat: implement json bindings for wrangler dev --local

[threepointone]

We implemented json bindings in #438, but we'll need it for --local mode as well. The complication here is that this is actually a proper breaking change, and might require changes in miniflare too, as well as some form of warning/messaging.

[JacobMGEvans]

Dependency: cloudflare/miniflare#218

[JacobMGEvans]

Considering the conversation (in miniflare#218), implementation of Miniflare API, I would like to consider reducing all the flag to --bindings which parses the TOML config still and remove the other flags, to more closely match how remote handles the bindings.

Cc: @petebacondarwin

[petebacondarwin]

@mrbbot suggested an alternative approach, which is to use Miniflare programmatically, where we have full access to set the bindings with the correct types.

[JacobMGEvans]

@mrbbot suggested an alternative approach, which is to use Miniflare programmatically, where we have full access to set the bindings with the correct types.

Correct. I was thinking about removing the extraneous flags and having the Miniflare programmatically (API) handle the TOML file vars and other bindings. Rather than always needing to add a flag when features are added, it would just consume the TOML file.

[petebacondarwin]

I believe this is now supported as of #633

[threepointone]

Should we just not have any messaging around the breaking change? Specifically, in wrangler1, x = 1 would previously have env.x be a string, and now it's a number. It might be fine, but something to remember.

[petebacondarwin]

I think the breaking change should have been with this change: 64d62be