oiiotool: Add --experimental command line argument. (#5147)

Introducing this as a way to allow us to have experimental oiiotool
features or behaviors that are enabled only if this flag is also
present.

It's a way of allowing features to be turned on for feedback before
we're sure it's in a form that can be a permanent, supported feature,
thus allowing it to undergo further change that is exempt from our usual
rules about what may change in which versions. By forcing users to also
employ this flag to enable the trial behavior, there's no way that they
can inadvertently come to depend on a temporary behavior and be
surprised if it changes later.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/doc/oiiotool.rst

@@ -988,6 +988,12 @@ subimage according to its metadata::
 
         oiiotool --oiioattrib debug 1 in.jpg -o out.jpg
 
+.. option:: --experimental
+
+    Enables experimental features. Use at your own risk.
+
+    This was added in OIIO 3.1.13.
+
 
 .. _sec-oiiotool-control-flow-commands:
 

src/oiiotool/oiiotool.cpp

@@ -6664,6 +6664,8 @@ Oiiotool::getargs(int argc, char* argv[])
     ap.arg("--nostderr", &ot.nostderr)
       .help("Do not use stderr, output error messages to stdout")
       .hidden();
+    ap.arg("--experimental", &ot.experimental)
+      .help("Allow experimental features");
 
     ap.separator("Control flow and scripting:");
     ap.arg("--set %s:NAME %s:VALUE")

src/oiiotool/oiiotool.h

@@ -83,6 +83,7 @@ class Oiiotool {
     bool nostderr        = false;  // If true, use stdout for errors
     bool noerrexit       = false;  // Don't exit on error
     bool create_dir      = false;
+    bool experimental    = false;  // Allow experimental features
     std::string dumpdata_C_name;
     std::string full_command_line;
     std::string printinfo_metamatch;