cmake: Add input redirection for script mode (-P)

This MR implements the input-redirection mode for cmake -P, as described in #23636.

Tests

A battery of tests are added to Tests/RunCMake/ScriptMode/ which cover the basic cmake -P - case, plus multiple other cmake -P scenarios including:

• Passing additional arguments before and after -P -
• Passing -DVAR=Value arguments, specifically, after -P -. (These will be ignored, just as they are by the current CMake. In a command like cmake -P script.cmake -DVAR=value, the -D argument is assumed to be a script argument, so it is not processed by cmake.)
• Running cmake -P - --trace
• Running cmake -P -DVAR=Value, because the error produced has changed.
  • Previously, it resulted in:

    CMake Error: No script specified for argument -P

  • With this change, the -D... argument is interpreted as the script filename:

    CMake Error: Error processing file: -DVAR=value

Fixes: #23636