feat(api): optional params after `opts` #40720

Problem:
After 25439dad7e2b, `opts` is optional, but not params that follow it.

Solution:
- Update `gen_api_dispatch.lua`, docs, tests.
- Enhance the `nvim_get_api_info()` api-metadata to include a boolean
  flag indicating whether a parameter is optional:
  ```
  [type, name, optional]
  ```

Note: Currently, optional params are assumed to be Dict/Array. Since we
don't yet have any use-cases of optional params following `opts`, the
build just checks this assumption and we can deal with it later if we
ever care to:

    nvim_get_hl: optional param "foo" has type "Integer" but (currently)
    we assume Dict/Array

0 files changed, 0 insertions, 0 deletions