[SYCL][E2E] Add RUN-IF lit keyword (#21288)
Add a new LIT keyword, `RUN-IF`, to simplify conditional commands in LIT
tests.
This is useful for when you have a single test but need to do different
things depending on the environment.
You can arleady to this today, but the syntax is verbose, something like
`RUN: %if condition %{ case %} %else %{ another_case %}`
We are planning to use the immediately in interop tests.
I modified some exists tests using the verbose syntax to lock down this
new syntax.
Signed-off-by: Nick Sarnie <nick.sarnie@intel.com>
