Support html formatter settings

[aeschli]

Testing microsoft/vscode#42361

Ideally, the html settings from VSCode would be used.

IMO the settings used required is "html.format.contentUnformatted" to control which tags should not be changed by the formatter.

[mjbvz]

Probably depends on microsoft/TypeScript#18604

Currently there is no way that I know of to pass configuration from VSCode to a TS Server plugin

[pdesjardins90]

@mjbvz The related PR was merged last week!

[zlldnv]

I will support it!:'(
It really needed

[mjbvz]

PRs welcome. Here's where we sync settings with the plugin:

vscode-lit-html/src/index.ts

Line 42 in 027f0ea

function getConfiguration(): SynchronizedConfiguration {

May also required some upstream changes the plugin: https://github.com/Microsoft/typescript-lit-html-plugin/blob/master/src/configuration.ts

Do people want separate html formatter settings for lit-html or should we re-use the normal html settings?

[sumbad]

@mjbvz I think lit-html has to re-use the normal html settings as usual *.html files.