Adding support for reading binary files in tool --function_input=. (#9328)

Raw binary data read from a file can now be used to initialize buffer
view contents. No interpretation is done on the data. The shape and
element type information is still required.

Example:
```
iree-benchmark-module ... --function_input=4x2xi32=@some/file.bin
```
diff --git a/tools/iree-benchmark-module-main.cc b/tools/iree-benchmark-module-main.cc
index d17d8e9..37619f8 100644
--- a/tools/iree-benchmark-module-main.cc
+++ b/tools/iree-benchmark-module-main.cc
@@ -124,6 +124,8 @@
     "  2x2xi32=1 2 3 4\n"
     "Optionally, brackets may be used to separate the element values:\n"
     "  2x2xi32=[[1 2][3 4]]\n"
+    "Raw binary files can be read to provide buffer contents:\n"
+    "  2x2xi32=@some/file.bin\n"
     "Each occurrence of the flag indicates an input in the order they were\n"
     "specified on the command line.");