remove type coercion from array values to references

[andrewrk]

Now that #265 is done, the main motivation for type coercion from array values to slices is gone. It's a footgun for Zig to automatically convert a value into a pointer to that value; such an operation should be explicit.

test "coerce array value to slice" {
    var array: []const i32 = [_]i32{ 1, 2, 3, 4 };
}

Expected output:

test.zig:2:30: error: expected type '[]const i32', found '[4]i32'
    var array: []const i32 = [_]i32{ 1, 2, 3, 4 };
                                   ^

Actual output: (test passes)

How to upgrade code for these new semantics:

-    var array: []const i32 = [_]i32{ 1, 2, 3, 4 };
+    var array: []const i32 = &[_]i32{ 1, 2, 3, 4 };

I expect this change to simplify the result location semantics, which should help with reasoning about zig code, as well as reduce the complexity of a zig compiler.

[andrewrk]

Implemented in #3787, landed in fecd540.