Allow true in more JML expressions

[mattulbrich]

Related Issue

This pull request resolves #3660.

Intended Change

See #3660 for details.

This fix allows true to be used as expression in more places in JML.

Type of pull request

• Bug fix (non-breaking change which fixes an issue)
• There are changes to the (Java) code

Ensuring quality

• I made sure that introduced/changed code is well documented (javadoc and inline comments).
• I added new test case(s) for new functionality. [to existing exprs.txt]

Additional information and contact(s)

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.06%. Comparing base (28025d8) to head (28d4dec).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3664      +/-   ##
============================================
- Coverage     47.16%   47.06%   -0.10%     
- Complexity    15801    15804       +3     
============================================
  Files          1673     1675       +2     
  Lines         96171    96331     +160     
  Branches      15397    15431      +34     
============================================
- Hits          45359    45339      -20     
- Misses        45641    45823     +182     
+ Partials       5171     5169       -2     

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