Option to disable ProofTree tooltips, render them lazily

[WolframPfeifer]

Trying to solve #3500, this PR does two things:

• It adds an option to disable the ProofTree tooltips, as requested for example by @unp1 and @mattulbrich. This option can be set in the options of the proof tree (gear icon) as well as in the global menu via "View" -> "Show ProofTree Tooltips" (where the SequentView and SourceView tooltips also can be toggled).
• A tooltip is now lazily rendered directly when it is needed, not already during creation of the GUITreeNode.

Related Issue

This pull request addresses #3500.

Type of pull request

• Bug fix (non-breaking change which fixes an issue)
• Refactoring (behaviour should not change or only minimally change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• There are changes to the (Java) code
• There are changes to the taclet rule base
• There are changes to the deployment/CI infrastructure (gradle, github, ...)
• Other:

Ensuring quality

• I made sure that introduced/changed code is well documented (javadoc and inline comments).
• I made sure that new/changed end-user features are well documented (https://github.com/KeYProject/key-docs).
• I added new test case(s) for new functionality.
• I have tested the feature as follows: manual inspection and testing in the GUI
• I have checked that runtime performance has not deteriorated.

Additional information and contact(s)

The contributions within this pull request are licensed under GPLv2 (only) for inclusion in KeY.

[WolframPfeifer]

@unp1 Could you maybe take a quick look whether this PR fixes your performance problems? I can not really reproduce them (at least, KeY does not seem slower than usual to me).

[WolframPfeifer]

I got the confirmation by @unp1 (thanks for testing!) that this fixes the performance problems, so I merge this now.

@unp1 By the way: I can not reproduce the problems with "Expand/collapse all". For me it works fine, regardless of the other view options which are set ("expand OSS", "hide intermediate", etc.).