Expressions: Add CHECK-DIAGS command to slang-lit; Move expression test

[AndrewNolte]

Stacked PRs:

• Structured Assigns: better diags #1927
• ->Expressions: Add CHECK-DIAGS command to slang-lit; Move expression test #1926
• Diagnostics: Put notes under associated diag for clients and json output #1925

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View individual changes

Expressions: Add CHECK-DIAGS command to slang-lit; Move expression test

This moves 'Assignment pattern errors' to the be a slang-lit test to show the diag ranges, and make updating expectations easier.
It also adds to the test to show some suboptimal diag ranges.

[codecov]

Codecov Report

❌ Patch coverage is 98.79518% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.06%. Comparing base (e3291f8) to head (310fdb9).

Files with missing lines	Patch %	Lines
source/diagnostics/DiagnosticEngine.cpp	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1926      +/-   ##
==========================================
+ Coverage   96.03%   96.06%   +0.03%     
==========================================
  Files         247      247              
  Lines       56855    56913      +58     
==========================================
+ Hits        54599    54675      +76     
+ Misses       2256     2238      -18     

Files with missing lines	Coverage Δ
include/slang/diagnostics/DiagnosticEngine.h	100.00% <100.00%> (ø)
include/slang/diagnostics/JsonDiagnosticClient.h	100.00% <ø> (ø)
include/slang/diagnostics/TextDiagnosticClient.h	100.00% <ø> (ø)
source/diagnostics/JsonDiagnosticClient.cpp	91.56% <100.00%> (+37.39%)	⬆️
source/diagnostics/TextDiagnosticClient.cpp	93.89% <100.00%> (+0.59%)	⬆️
source/diagnostics/DiagnosticEngine.cpp	91.46% <97.22%> (-0.19%)	⬇️

... and 2 files with indirect coverage changes

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[MikePopoloski]

I don't really want all of these tests moved over in one giant chunk. There's no way I can review these to make sure nothing got dropped or changed, and debugging the regression tests is slightly more annoying than with the in-process unit tests. If you want to put new tests and/or move a few specific ones over that's fine.

[AndrewNolte]

Will amend to just the one on the following pr