Add BIconUtils::GetSystemIcon

Allow to easily access the alert icons and anything that's added to app_server
resources.

Fixes #10887.

Convert BAlert, Debugger AlertWithCheckbox and Keymap ModifierKeysWindow
to make use of it, removing the duplicate code to locate app_server
resources.

The resources are initialized only once (per application), so there is no need
to reload them for every access to the icons.

In the ticket there is discussion about putting this in BControlLook,
but I think this should in fact be moved fully into app_server with
special drawing commands for well-known icons. That would avoid loading
and rendering the icon on the application side to then send it to
app_server (especially in remote_app_server case)?

In any case, this simple API can serve as a base for applications to
use, and we can change how it is implemented later on.

Change-Id: Id370526ae5cf165cfb8bc277bc8a7f46c26f542d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6463
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Debugger: fix empty button on alerts with only 2 buttons

When no debuginfo is available from packages, the alert has only two
buttons. This was not handled correctly, leading to a small empty button
being present.

Change-Id: I44de1101f7cd539da5c582eaf34bb1476aa9ab20
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6462
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

Debugger: fix width of alert for short messages

Don't force a larger min size if the message is short enough.

To do this:
- Get the TextRect without word wrapping
- If that is small enough, nothing to do
- If that is too wide, set a minimal size that will be used for the word wrapping so the alert
doesn't get too large and also doesn't get too narrow

Fixes #18404

Change-Id: Iee2704377180510edf7bdf930583b8a7cc47ef2e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6461
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

Debugger: add a "don't ask again" checkbox to alerts

This allows, for example, to skip all the "get debug info" alerts when
starting a debug session. But it is a generic implementation and will
work for all "question" alerts in Debugger.

For now, the user choices are not saved, this could be done, but then we
need a way to access that setting later.

Fixes #14601

Change-Id: Icc49d1b5bc4168d15d7f740d422f464e996f7c9d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6398
Reviewed-by: waddlesplash <waddlesplash@gmail.com>