fix(validation): type-check variable initializers (1.0.x)

[ghaith]

Backport of #1924 to release/1.0.x.

Problem: An initializer whose type cannot be assigned to the declared variable type, such as x : STRING := 3 or a : DINT := TRUE, passes --check and aborts later in code generation or silently stores a converted value. Only body assignments ran the assignment type check; VAR, VAR_GLOBAL, function block members and struct members were never validated, while VAR_TEMP was caught by accident through its lowered copy and reported without a source location. BOOL was treated as a numeric value everywhere, so DINT := TRUE and DINT#TRUE were accepted in bodies too, and array literal elements were never checked against the element type, so ARRAY[0..1] OF REAL := [TRUE, FALSE] panicked in code generation.

Solution: Run the same assignment validation on every variable initializer and on every element of an array literal, so declarations and body assignments report identical diagnostics (E037 mismatches, E067 downcasts). A BOOL value assigned to another numeric type is now an invalid assignment, as is an integer literal other than 0 or 1, or a real literal, assigned to a BOOL; BOOL := 1 stays valid. A BOOL literal behind a numeric type prefix (DINT#TRUE) is an incompatible literal cast like DINT#1.5, and BOOL#TRUE now evaluates as a constant initializer. The standard library's BOOL_TO_<integer> functions use the explicit IF form already used for the bit conversions, and the CFC storage test on a numeric sink now asserts the rejection. The lowered copies of initializers are skipped so each mismatch is reported once, at its declaration. Pointer-typed declarations accept pointer and integer initializers for now; any other value, such as a string or a real, is rejected like in a body, and a REF_TO initializer whose target type differs reports the same E090 warning as the body form instead of an error. Inline pointer types no longer include their initializer in the location used for type names. Numeric array literal elements are cast to the array's element type in code generation, so accepted conversions such as ARRAY OF INT := [1.5, 2] no longer panic.

Refs: PRG-4728

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