gcc-arm-embedded: Update to 11.3.rel1 and package structure changes

[Kreeblah]

Important: Do not tick a checkbox if you haven’t performed its action. Honesty is indispensable for a smooth review process.

In the following questions <cask> is the token of the cask you're submitting.

After making all changes to a cask, verify:

• [x] The submission is for a stable version or documented exception.
• [x] brew audit --cask --online <cask> is error-free.
• [x] brew style --fix <cask> reports no offenses.

Note: I removed the zap stanza because there doesn't seem to be a reasonable way to do it for this package without potentially impacting an installed copy of the gcc-aarch64-embedded cask once it's updated. I believe the updated package for that one will also install into /Applications/ArmGNUToolchain/#{version}, but in a different subdirectory.