Fix CI failures: update neg116/neg117 baselines, skip IWSAM on net48, suppress warning 52

4 CI failures fixed:

1. neg116.bsl/neg117.bsl: These tests expected 'ilxgen error FS0041' but now
   compile successfully. The RFC FS-1043 constraint solver changes fix a
   pre-existing codegen bug where trait calls failed to resolve at IL generation.
   Updated baselines to empty (compilation succeeds, ILVerify passes).

2. IWSAM extension wins test: Uses 'static abstract member' (IWSAM) which is
   not available on .NET Framework (net48). Added #if !NETCOREAPP Skip.

3. DateTime plus y test: Warning 52 (defensive copy of value type) treated as
   error on net48. Added --nowarn:52.

4. Gate stripTyEqnsAndMeasureEqns behind ExtensionConstraintSolutions feature
   flag to avoid changing observable semantics for non-preview langversions.

Why not spotted locally: neg116/neg117 are legacy tests skipped on macOS/Linux.
IWSAM/DateTime tests pass on net10.0 but fail on net48 (CI-only configuration).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: T-Gro