Fold the three anti-aliasing functions into one

[MAX-WiRED]

The waveform's anti-aliasing is three functions that differ only in how many
samples they average:

    void antiAlias2x(uint8_t* dst, int w, int h) { ... }
    void antiAlias3x(uint8_t* dst, int w, int h) { ... }
    void antiAlias4x(uint8_t* dst, int w, int h) { ... }

picked by a switch that has to grow an arm for every factor.

The change

One loop covers every factor:

    void antiAlias(uint8_t* dst, int w, int h, int factor) {
        const int newW = w / factor, newH = h / factor;
        const int area = factor * factor;
        ...
    }

and the switch becomes

    if (getAntiAliasing() > 0) {
        antiAlias(texBuf, w, h, getAntiAliasing() + 1);
    }

The three named functions and the switch go. Nothing else about how a block is
rendered changes.

The list of settings is untouched: None, 2x, 3x, 4x, as before. The
clamp that used to sit at the call site in loadSettings moved into
setAntiAliasing, so the bound is written once as NUM_AA_MODES rather than
as a bare 3.

Testing

Built on Windows with clang-tidy and clang-format enforced, as the build does.

Walked the setting from None to 4x on a song with real audio: the list reads
as it did, the waveform redraws at each step, and 2x, 3x and 4x look the
way they did before the change.

[Psycast]

Personally anything past 4x is already past diminishing returns on quality, and is substantially more compute intensive.

[uvcat7]

Refactoring the code to remove the three nearly-duplicate functions is worth it. But keep the max antialiasing at 4, please!

[uvcat7]

Thanks! Just need to fix this one thing.

[uvcat7]

Remove this function please and replace its calls with getAntiAliasing.