* gdb: Clarify a comment
* gdb: Fix gdb.unwinder.Unwinder.__call__ argument. It takes a gdb.PendingFrame, not a gdb.Frame.
* gdb: Unwinders may implement a proto without subclassing gdb.unwinder.Unwinder
* gdb: Fix Breakpoint.__init__
1. `line` should be `int|str`, not just `int` (IDK what a string means,
but that it can be a string is clear if you read
py-breakpoint.c:bppy_init().
2. `type` argument should be able to be passed to the "location" form,
not just the "spec" form, even if
https://sourceware.org/gdb/current/onlinedocs/gdb.html/Breakpoints-In-Python.html
neglects to mention it (don't worry, I'll be submitting a patch to fix
the doc soon).
3. Fix the positional argument order (based on GDB's sources, it isn't
really documented)
4. Use more `@overloads` to enforce that at least 1 of `function`,
`label`, or `line` are given in the location form.
When GDB has just started, several `gdb` submodules are automatically
loaded, so user code does not have to manually import them (for instance
`import gdb.events`). Reflect that in `gdb` stubs.
* gdb.events.BreakpointEvent: fix various typos
* gdb.printing: remove GenPrinterFunction
This was meant to be a private type alias, but it is unused and a
duplicate of the better named gdb._PrettyPrinterLookupFunction.
