Add ShellCheck's "source.fixAll.shellcheck" functionality

[j-lakeman]

What is the problem this feature will solve?

lots of little bash problems at once e.g. forgotten quotation marks

What is the feature you are proposing to solve the problem?

automatic fixing of simple issues on save e.g. inserting quotation marks

What alternatives have you considered?

Using ShellCheck alongside Bash IDE, but only for this functionality, as Bash IDE already has all of ShellCheck's other features. This would implement one more quite handy little feature IMHO.

[chrisgrieser]

I agree. To truly make bash-lsp standalone, it would also require bundling shellcheck though (#663)

[skovhus]

Makes sense. Contributions are more than welcome.