Adopt improved DocumentSymbolProvider API

[fbricon]

A DocumentSymbolProvider should now return document symbols which can represent a hierarchy and that can differentiate between the full range of a symbol and the selection range, e.g. the name of a function.

The API is already available in LSP4J (0.5.0).

[kittaakos]

This LSP4J issue might affect this task: eclipse-lsp4j/lsp4j#252. I am waiting for confirmation.

[kittaakos]

@fbricon, I start working on this issue. Please assign this to me. Thank you!

[kittaakos]

This requires bumping up LSP4J to the 0.5.0.v20180903-1212 release. 0.5.0has API changes:

• o.e.lsp4j.services.TextDocumentService#codeAction(o.e.lsp4j.CodeActionParams)
• o.e.lsp4j.services.TextDocumentService#documentSymbol(o.e.lsp4j.DocumentSymbolParams)

I will work on the documentSymbol in the scope of this task, but the codeAction, I just adjust to compile. This means, CodeAction will not be supported.

[fbricon]

@kittaakos lsp4j 0.5.0.M1 is now in use. You can start playing :-)

[kittaakos]

I found an inconsistency between the JDT UI code and the code we have copied into JDT LS.
According to the JDT UI code, the JavaElementLabels.DECL_STRING should be " :" (see the leading whitespace).

https://github.com/eclipse/eclipse.jdt.ui/blob/6dfe33cd6d1478e9ebb5819c42945dcb78acae61/org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/JavaElementLabels.java#L366

https://github.com/eclipse/eclipse.jdt.ui/blob/6dfe33cd6d1478e9ebb5819c42945dcb78acae61/org.eclipse.jdt.core.manipulation/common/org/eclipse/jdt/internal/core/manipulation/JavaElementLabelsCore.java#L344

https://github.com/eclipse/eclipse.jdt.ui/blob/6dfe33cd6d1478e9ebb5819c42945dcb78acae61/org.eclipse.jdt.core.manipulation/common/org/eclipse/jdt/internal/core/manipulation/JavaElementLabelsMessages.properties#L21

It is ":" (without the leasing whitespace) in JDT LS.

I am going to change it and fix if there are no objections.

Also, I am going to add the type information of the return type to the method names.

Before:

After:

[kittaakos]

PR: #792