Update language guide(s) for 3.0

[lann]

Spin 3.0 is dropping support for uncomponentized modules, which impacts some language guides:

• Grain
  • Component support is experimental in Grain; see grain-lang/grain#2153
  • Need to update example; see updated template: https://github.com/fermyon/spin/pull/2789/files#diff-01f53c72a892731d7a1f85440a7e0050f810b51541174615f3ea901fbe10e466
  • Build command needs to change: grain compile --release --use-start-section ...
• Swift
  • Dropping support in Spin 3.0 due to the currently-released SwiftWasm 5.10's very old version of wasi-libc.
  • Support is likely to be possible again when Swift 6.0 is released
• Others? Might be good to review some of the more obscure langauges...