Find implementation intelligently fall back to find definition

[testforstephen]

Signed-off-by: Jinbo Wang [email protected]

Fix #1098

If the find implementation happens at the position of method or type declaration, keeps old behavior.

If it happens at the position of method/type invocation, then follows the rules below to determine whether to include the definition to the result.

• If the hovered element is an unimplemented member (abstract or interface) and no implementations are found in the workspace, then include the element definition to the result.
• If the hovered element is non abstract or interface, then always include the element definition as the first result.

[testforstephen]

test this please

[testforstephen]

test this please

[fbricon]

Thanks @testforstephen !