Add SPISettings while keeping __SPISettings as an alias for wiring layer

[keeramis]

Problem

__SPISettings naming is not compatible with Arduino layer

Solution

Rename __SPISettings to SPISettings and still keep __SPISettings as an alias

Steps to Test

Existing unit tests, but also something like this app should compile without errors

#include "application.h"

void setup() {
    int32_t r = SPI.beginTransaction(__SPISettings(SPI_CLK_SYSTEM, SPI_MODE0, MSBFIRST));
    (void)r;
    int32_t r2 = SPI.beginTransaction(SPISettings(SPI_CLK_SYSTEM, SPI_MODE0, MSBFIRST));
    (void)r2;
}

void loop() {
}

References

ch55527
ch54115

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[keeramis]

There are also multiple locations __SPISettings can be changed, and potentially add unit tests for SPISettings instead of / in addition to __SPISettings, but don't think it is needed to change/add this every where.

[avtolstoy]

I'm approving the change, but we should fix all the tests that use __SPISettings as well.