Add --canary option to build web compilers

[annagrin]

Add canary option for build_web_compilers:ddc and build_web_compilers:sdk_js builders to enable canary features in DDC.

This setting is disabled by default but can be enabled by setting it to true globally:

global_options:
  build_web_compilers:ddc:
    options:
      canary: true
  build_web_compilers:sdk_js:
    options:
      canary: true

Closes: #3535

[annagrin]

@natebosch @jakemac53 I had to add --canary option to ddc and sdk_js builders in web_dev_compilers, as they have to match. Is there a way to set this option in a better way - i.e for the whole set of web_dev_compilers builders?

[annagrin]

Looks like a new warning, wasn't sure this API is used at runtime somewhere so I hesitated to remove it:)

[natebosch]

Ignoring it is the correct thing to do for now. It looks to me like a bug in the lint.

https://github.com/dart-lang/linter/issues/4495

[jakemac53]

@natebosch @jakemac53 I had to add --canary option to ddc and sdk_js builders in web_dev_compilers, as they have to match. Is there a way to set this option in a better way - i.e for the whole set of web_dev_compilers builders?

You have to do them separately like you have here

[jakemac53]

If you need this published soon go ahead and drop the -wip

[annagrin]

If you need this published soon go ahead and drop the -wip

Done!