Hackeython unknown methods

Related Issue

This pull request addresses #1663

Intended Change

When using a library method without an explicit contract, instead of getting stuck in the proof, KeY now assumes the following default contract

public behavior
    ensures true;
    diverges true;
    signals_only Throwable;
    assignable \everything;

In addition, there is a proof setting soundDefaultContracts which can be turned off. In this case, the following default contract is used instead, which may be useful for exploratory proofs

public normal_behavior
    ensures true;
    assignable \strictly_nothing;

Type of pull request

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] Refactoring (behaviour should not change or only minimally change)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[x] 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

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

Additional information and contact(s)

This was done during HacKeYThon 2 by @JonasKlamroth and @flo2702

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

Codecov Report

Attention: Patch coverage is 60.52632% with 15 lines in your changes missing coverage. Please review.

Project coverage is 37.77%. Comparing base (1b48b9e) to head (04cc9ed). Report is 56 commits behind head on main.

:exclamation: Current head 04cc9ed differs from pull request most recent head 028663e

Please upload reports for the commit 028663e to get more accurate results.

Files	Patch %	Lines
...d/key/speclang/jml/translation/JMLSpecFactory.java	53.57%	12 Missing and 1 partial :warning:
...main/java/de/uka/ilkd/key/speclang/SLEnvInput.java	77.77%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3431 +/- ## ============================================ - Coverage 38.03% 37.77% -0.26% + Complexity 17089 17039 -50 ============================================ Files 2099 2076 -23 Lines 127274 126988 -286 Branches 21386 21387 +1 ============================================ - Hits 48409 47975 -434 - Misses 72892 73104 +212 + Partials 5973 5909 -64 ```

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KeYProject / key