Fix FitsIn(tree->TypeGet(), value) assert

[EgorBo]

Fixes #113940

[EgorBo]

/azp run Fuzzlyn

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Pull Request Overview

This PR fixes an assertion failure related to FitsIn(tree->TypeGet(), value) by adjusting the condition for casting small variable constants in the assertion propagation logic.

• Removed the check for op1 being a store-local-var, now applying optCastConstantSmall whenever the local variable type is small.
• Updates the assertion creation logic in assertionprop.cpp to address the reported issue.

Comments suppressed due to low confidence (1)

src/coreclr/jit/assertionprop.cpp:1245

• Removing the op1->OperIs(GT_STORE_LCL_VAR) condition could potentially lead to casting being applied in contexts where it was not previously intended. Please verify that this change does not introduce side effects in non-store local variable scenarios by expanding the test coverage if necessary.

if (varTypeIsSmall(lclVar))