[scss] support @forward 'library' with syntax

[lekoala]

Version: 1.43.0 (system setup)
Commit: 78a4c91
Date: 2020-03-09T19:47:57.235Z
Electron: 7.1.11
Chrome: 78.0.3904.130
Node.js: 12.8.1
V8: 7.8.279.23-electron.0
OS: Windows_NT x64 10.0.18362
(i can also provide extensions but I don't think it really matters in this case)

Steps to reproduce

Open a .scss file
copy paste this

@forward 'library' with (
$black: #222 !default,
$border-radius: 0.1rem !default
);

Expected result : no problems
Actual result:
{
"resource": ".../sass/all.scss",
"owner": "generated_diagnostic_collection_name#0",
"code": "css-unknownkeyword",
"severity": 8,
"message": "unknown keyword",
"source": "scss",
"startLineNumber": 3,
"startColumn": 20,
"endLineNumber": 3,
"endColumn": 24
}

So it seems the sass module system (@use/@Format) should be supported, but the support seem incomplete

The following examples do not work

@forward 'library' with (
  $black: #222 !default,
  $border-radius: 0.1rem !default
);

or

@use 'library' with (
    $black: #222 !default,
    $border-radius: 0.1rem
);

it seems support is missing for:

• @forward with configuration
• @use with !default in the configuration (@use with configuration without !default works fine)

[lekoala]

Version: 1.43.0 (system setup)
Commit: 78a4c91
Date: 2020-03-09T19:47:57.235Z
Electron: 7.1.11
Chrome: 78.0.3904.130
Node.js: 12.8.1
V8: 7.8.279.23-electron.0
OS: Windows_NT x64 10.0.18362
(i can also provide extensions but I don't think it really matters in this case)

Steps to reproduce

1. Open a .scss file
2. copy paste this
   @forward 'library' with (
   $black: D language support #222 !default,
   $border-radius: 0.1rem !default
   );

Expected result : no problems
Actual result:
{
"resource": ".../sass/all.scss",
"owner": "generated_diagnostic_collection_name#0",
"code": "css-unknownkeyword",
"severity": 8,
"message": "unknown keyword",
"source": "scss",
"startLineNumber": 3,
"startColumn": 20,
"endLineNumber": 3,
"endColumn": 24
}

[SharakPL]

Also !default is missing from the suggestions