Support implicit conversion of Int4 component to Int
Support implicit conversion of Int4 component to Int

Previously we needed Int(v.x) syntax to assign a component of an Int4
vector to an Int scalar variable, which was needlessly verbose. We
already supported implicit conversion of Float4 components to Float.

Bug: b/221072484
Change-Id: If0ee20eecf0fa35f669099c2b04ab590c1830068
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/63289
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,google/swiftshader,google/swiftshader