Use @fluent/dedent

Hi @eemeli 👋 I noticed that you implemented a dedentation helper in:

Lines 16 to 24 in 63c40ff

    
           export function ftl(strings) { 
        
             const [code] = strings 
        
             const lines = code.split('\n').slice(1, -1) 
        
             const indents = lines.filter(nonBlank).map(countIndent) 
        
             const common = Math.min(...indents) 
        
             const indent = new RegExp(`^\\s{${common}}`) 
        
             const dedented = lines.map(line => line.replace(indent, '')) 
        
             return `${dedented.join('\n')}\n` 
        
           }

Not too long ago I extracted and refactored the ftl helper into its own package: https://github.com/projectfluent/fluent.js/tree/master/fluent-dedent

Perhaps you'd like to switch to it? I can create a pull request, if you wish.

Sure, I'm fine with switching, and would welcome a PR.

FYI, the dedenter is only used in the tests, and it probably cleans up leading & trailing empty lines a bit differently than @fluent/dedent. I also just pushed a bunch of changes that bring the implementation in line with projectfluent/fluent.js#380, in case you start working on this.

	export function ftl(strings) {
	const [code] = strings
	const lines = code.split('\n').slice(1, -1)
	const indents = lines.filter(nonBlank).map(countIndent)
	const common = Math.min(...indents)
	const indent = new RegExp(`^\\s{${common}}`)
	const dedented = lines.map(line => line.replace(indent, ''))
	return `${dedented.join('\n')}\n`
	}