Useful for lazily building a new `File` if it hasn't been registered already.

Also assign the file to the location of a new frame. This is a sensible default to have.

Bug: b/145351270
Change-Id: I7c0abff22a0010923428ff5ed0760d6ae63b0c6b
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48697
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>