Changes

[ARM] Update isVMOVNOriginalMask to handle single input shuffle vectors

The isVMOVNOriginalMask was previously only checking for two input
shuffles that could be better expanded as vmovn nodes. This expands that
to single input shuffles that will later be legalized to multiple
vectors.

Differential Revision: https://reviews.llvm.org/D94189

[obj2yaml,yaml2obj] - Refine how we set/dump the sh_entsize field.

This reuses the code from yaml2obj (moves it to ELFYAML.h).
With it we can set the `sh_entsize` in a single place in `obj2yaml`.

Note that it also fixes a bug of `yaml2obj`: we do not
set the `sh_entsize` field for the `SHT_ARM_EXIDX` section properly.

Differential revision: https://reviews.llvm.org/D93858

[clang][driver] Restore the original help text for `-I`

The help text for `-I` was recently expanded in [1]. The expanded
version focuses on explaining the semantics of `-I` in Clang. We are now
in the process of adding support for `-I` in Flang and this new
description is incompatible with the semantics of `-I` in Flang. This
was brought up in this review:
  * https://reviews.llvm.org/D93453

This patch reverts the original change in Options.td. This way the help
text for `-I` remains generic enough so that it applies to both Clang
and Flang.

The expanded description of `-I` from [1] is moved to the
`DocBrief` field for `-I`. This field is prioritised over the help text
when generating ClangCommandLineReference.rst, so the user facing
documentation for Clang retains the expanded description:
  * https://clang.llvm.org/docs/ClangCommandLineReference.html
`DocBrief` fields are currently not used in Flang.

As requested in the reviews, the help text and the expanded description
are slightly refined.

[1] Commit: 8dd4e3ceb804a58bcf25e6856fc6fde5e1995a66

Differential Revision: https://reviews.llvm.org/D94169