common/input: Avoid numerous large copies of CallbackStatus

input/SDL: Update SDL hints

SDL_HINT_JOYSTICK_HIDAPI_SWITCH_HOME_LED is no longer needed thanks to new default in SDL 2.0.18.
SDL_HINT_JOYSTICK_HIDAPI_XBOX is reported to cause conflicts with native driver Xbox driver on Linux, and Xbox controllers don't benefit from hidapi anyways.

input_poller/input_mapping: Silence several -Wdocumentation warnings

CallbackStatus instances aren't the cheapest things to copy around
(relative to everything else), given that they're currently 520 bytes in
size and are currently copied numerous times when callbacks are invoked.

Instead, we can pass the status by const reference to avoid all the
copying.

Given these return void, these can be omitted.

param tags are supposed to specify the parameter name without any
quoting.

Silences several -Wdocumentation warnings.

Silences quite a bit of -Wdocumentation warnings, given the @param tag
is only intended to be used to identify function parameters, not what it
contains.

input_engine: Minor object churn cleanup

tas_input: Minor cleanup

We don't need to copy the whole pair

Resolves a -Wextra-semi warning

clear() when empty is simply a no-op, so we can get rid of the check
here and let the stdlib do it for us.

Gets rid of indirect includes and includes only what the interface
needs.

While we're in the same area, we can also avoid performing std::stoi in
a loop when it only needs to be performed once.

This is only using the input facilities, so we don't need to use the
fully-fleged stringstream.

Same behavior, but without the potential for extra allocations.

This also means we can get rid of the dependency on <regex>

Parameters shouldn't have the colon by their name.

Prevents these values from potentially clashing with anything in other
headers.

We can make use of try_emplace() to insert values only if they don't
already exist.

We can use iterators to avoid looking up into maps twice in the getter
functions.

At the same time we can also avoid copying the ControllerData structs,
since they're 264 bytes in size.

These types are part of the InputCommon namespace.

Avoids creating copies of several object instances (some of which being
over 100 bytes in size).

Copies the BasicMotion instance once instead of twice.

Allows avoiding std::function allocations.

Avoids copies where reasonably applicable

Avoids creating copies of the struct where not necessary.

We can allow the name to be moved into, allowing allocations to be
avoided.

The callback map is a member variable, so this will always be empty on
initial construction.

Silences -Wextra-semi warnings

This is a void function, so it doesn't need this.

Remove erroneous #pragma once

build: remove remaining bits of Unicorn

build: update cubeb and remove the result_of comment

Kernel: Improve threading & scheduling V3

Unicorn has been removed in fc6db97a