Support switching to/from custom views in reference-view API

[CsCherrYY]

Signed-off-by: Shi Chen chenshi@microsoft.com

This PR fixes #146037

see also: microsoft/vscode-references-view#74, microsoft/vscode-references-view#75

With this change, we can

• pass an anchor (vscode.Location exactly) to the current setTypeHierarchyDirection() to manipulate the preset type views (supertype view and subtype view). see https://github.com/CsCherrYY/vscode-java/blob/bff041f997a6de0cbba9df243c1b7dc3a6f84006/src/standardLanguageClient.ts#L421-L427 for the usage.
• have a way to get the current valid anchor of the reference-view, it helps to switch to our custom reference views from the preset reference views (supertype view and subtype view). see https://github.com/CsCherrYY/vscode-java/blob/bff041f997a6de0cbba9df243c1b7dc3a6f84006/src/typeHierarchy/typeHierarchyTree.ts#L76-L83 for the usage.

[jrieken]

Sorry - I have been swapped recently and I am now heading out to a longer vacation. My plan is to finally pick this up in August. Thanks for being patient and happy coding

[CsCherrYY]

@jrieken never mind, enjoy your vacation!😀

[jrieken]

Thanks and sorry for the huge delay here