Improve install instructions for macOS

[rgov]

Summary

Several improvements to the install instructions for macOS including,

• Using curl instead of wget, which is not built-in.
• Unifying environment variable settings between Intel and Apple Silicon Macs.
• Instructing the user how to install the Xcode Command Line Tools.
• Directing users to the Homebrew documentation rather than duplicating it.
• Prioritizing Zsh (the default shell) over Bash.
• Partially addresses Change references from OS X to macOS  #106.

I've only made the changes to Harmonic so far, but once approved they can be applied to Ionic as well.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[scpeters]

Thanks for your contribution! As you said, there are a lot of different changes in this pull request, some of which I am ready to approve immediately, but others will require more discussion. In particular, I am ready to immediately approve the following changes:

• Using curl instead of wget, which is not built-in.
• Partially addresses Change references from OS X to macOS  #106.

if you want to split these out into a separate pull request and propagate the changes to other documentation files, I'll be happy to review it

[scpeters]

I'm not sure why you changed the syntax to ${CMAKE_PREFIX_PATH:+$CMAKE_PREFIX_PATH:}. I think it's easier to read the original syntax. I also think it's a little easier to read the $(...) instead of backticks

Suggested change

	export CMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH:+$CMAKE_PREFIX_PATH:}`brew --prefix qt@5`
	export CMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}:$(brew --prefix qt@5)

[rgov]

${CMAKE_PREFIX_PATH:+$CMAKE_PREFIX_PATH:} is the unfortunate shell (Bash, Zsh) syntax for "append a : delimiter after the variable if it has a value". Otherwise if CMAKE_PREFIX_PATH is not set and you write ${CMAKE_PREFIX_PATH}:/opt/homebrew you get :/opt/homebrew.

[scpeters]

@j-rivero I'll let you merge this since it may conflict with #451