feat: support referencing local variables in pointer initialization

[mhasel]

Adds support to initialize pointer, alias and reference-to variables with the address of local POU members.
The only exception is that stateful members cannot be initialized with addresses of temporary values, since 1) they do not exist at the time of initialization and 2) would lead to dangling pointers after going out of scope.

[codecov]

Codecov Report

Attention: Patch coverage is 93.83562% with 9 lines in your changes missing coverage. Please review.

Project coverage is 91.41%. Comparing base (be78df6) to head (0c4c94e).
Report is 115 commits behind head on master.

Files with missing lines	Patch %	Lines
src/validation/variable.rs	90.24%	4 Missing ⚠️
compiler/plc_driver/src/lib.rs	66.66%	3 Missing ⚠️
src/codegen/generators/expression_generator.rs	0.00%	1 Missing ⚠️
src/lowering.rs	98.24%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1346      +/-   ##
==========================================
+ Coverage   91.11%   91.41%   +0.29%     
==========================================
  Files         153      160       +7     
  Lines       44816    49660    +4844     
==========================================
+ Hits        40833    45395    +4562     
- Misses       3983     4265     +282     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[volsa]

Looks good, just missing a new error code

[volsa]

Nice!