Add build support for watchOS

[atlassian-psaha]

What does this PR do?
Adds support for building for watchOS

Where should the reviewer start?
At the definitions / conditionals changed for watchOS

How should this be manually tested?
Compile for watchOS

Any background context you want to provide?
Required for watchOS

What are the relevant tickets?
n/a

Screenshots or screencasts (if UI/UX change)

Questions:

• Does the docs need an update? Adds watchOS support
• Are there any security concerns? no
• Do we need to update engineering / success? no