Fixes#11324.
* Always `cd "$THIS_SCRIPT_PATH"`
* Remove unnecessary `cd` from all build.sh
* Remove unnecessary `set -eu` from all build.sh (and `# set -x`)
* Replace old build-utils.sh incantation in a few build.sh scripts
Because we don't know if mac BSD cp or GNU cp will be first on the path,
where there is ambiguity (e.g. with -R flag), we will use the macOS cp
command in /bin to ensure that we have consistent results. The
alternative would be to fixup each instance of the cp parameters so that
they work consistently with either cp command, but given these scripts
can run only on macOS, that seems unnecessary.
This replaces the earlier change in 97c6331b5.
Fixes up scripts (except under /linux) to use `#!/usr/bin/env bash`
instead of `#!/bin/bash` or `#!/bin/sh` so that we don't end up with
the ancient version of bash supplied with macOS.
This became urgent with this PR, because of bash-4.xisms in
build-utils.sh, for example on line 572:
```
if [[ -v _builder_params[$e] ]]; then
```
Adds run-xcodebuild function to wrap xcodebuild calls to keep logging
and error handling consistent. Currently used only by the iOS build; the
macOS build has a corresponding execBuildCommand function which does
pretty much the same thing (changing that would belong in a separate PR
I think and low priority.)
When working on a new build script, I tripped over the `-?` question
mark help parameter here, as it needs to be escaped. Opted to fix all
the instances in our scripts, although AFAICT there would not have been
current bugs arising from this, as there were no conflicting one
character options lower in the case list.
