Support xml.format.enforceQuoteStyle setting with experimental formatter

[angelozerr]

See https://github.com/redhat-developer/vscode-xml/blob/master/docs/Formatting.md#xmlformatenforcequotestyle

[angelozerr]

@JessicaJHee are you interested in working on this issue?

[JessicaJHee]

Yes looks interesting!

[angelozerr]

@JessicaJHee for the test I have copy/pasted the test from the old formatter in https://github.com/eclipse/lemminx/blob/master/org.eclipse.lemminx/src/test/java/org/eclipse/lemminx/services/format/experimental/XMLFormatterQuoteStyleTest.java

All tests are disabled https://github.com/eclipse/lemminx/blob/a099dc2953cc6d87babec769d108b6c8274b26ae/org.eclipse.lemminx/src/test/java/org/eclipse/lemminx/services/format/experimental/XMLFormatterQuoteStyleTest.java#L31

The main idea is to

• remove those @disabled annotation once you will support corectly quote.
• the last line of your test must be assertFormat(expected, expected, settings); it means that the format of expected content should not changed and no text edit should be generated. You can see that for other tests like https://github.com/eclipse/lemminx/blob/a099dc2953cc6d87babec769d108b6c8274b26ae/org.eclipse.lemminx/src/test/java/org/eclipse/lemminx/services/format/experimental/XMLFormatterExperimentalIndentTest.java#L36