Add @checked annotations to secondlife.d.luau

[tapple]

• Part of Create a generator for EmbeddedBuiltinDefinitions.cpp #122

Functions marked @checked has run-time type checks that match the typechecker. These functions report the same errors in --!strict and --!nonstrict modes.

I ran into a luau bug during this PR, and had to add a few ugly workarounds to the generator: luau-lang/luau#2384

I wanted to add @checked to functions in the ll module, but, I'm delaying that to a future PR for the following reasons:

1. that would approximately triple the size of this PR.
2. I'm unsure if i wanted to add @checked in the generator, or in the lsl_definitions.yaml file
3. I need to better understand/document what @checked does so I can think about it for each ll function. I expect most or all ll functions will want @checked, but, I need to think about that another time
4. I'd rather get to generating EmbeddedBuiltinDefinitions.cpp sooner rather than later, and this isn't really critical for that