[rtext] Don't call TextLength in DrawTextEx and MeasureTextEx

[Peter0x44]

Currently, DrawTextEx and MeasureTextEx call TextLength first to scan for the null terminator, before beginning a loop on all of the codepoints. Instead, check for the null terminator during the loop.

[raysan5]

This change increase code complexity on basic raylib functions, I need to think about it, did you measure the performance gain?

[asdqwe]

Out of curiosity, did this test:

#include "raylib.h"
int main(void) {
    InitWindow(800, 450, "test");
    SetTargetFPS(60);
    while (!WindowShouldClose()) {
        BeginDrawing();
        ClearBackground(RAYWHITE);

        double begin = GetTime();
        for (int i = 0; i < 40; i++) { DrawTextEx(GetFontDefault(), "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.", (Vector2) { 0, i*10 }, 10.0f, 1.0f, BLACK); }
        double end = GetTime();
        TraceLog(LOG_INFO, "time:%f", (end - begin));

        EndDrawing();
    }
    CloseWindow();
    return 0;
}

Got this results for `PLATFORM_DESKTOP_GLFW` on Linux Mint 22.0:

Results for current master branch:

INFO: time:0.005673
INFO: time:0.005729
INFO: time:0.005710
INFO: time:0.005678
INFO: time:0.005810
INFO: time:0.005697
INFO: time:0.005680
INFO: time:0.005732
INFO: time:0.005714
INFO: time:0.005826
INFO: TEXTURE: [ID 2] Unloaded texture data from VRAM (GPU)
INFO: SHADER: [ID 3] Default shader unloaded successfully
INFO: TEXTURE: [ID 1] Default texture unloaded successfully
INFO: Window closed successfully

Results for this PR:

INFO: time:0.005657
INFO: time:0.005714
INFO: time:0.005699
INFO: time:0.005657
INFO: time:0.005687
INFO: time:0.005702
INFO: time:0.005652
INFO: time:0.005712
INFO: time:0.005709
INFO: time:0.005660
INFO: TEXTURE: [ID 2] Unloaded texture data from VRAM (GPU)
INFO: SHADER: [ID 3] Default shader unloaded successfully
INFO: TEXTURE: [ID 1] Default texture unloaded successfully
INFO: Window closed successfully

Got this results for `PLATFORM_WEB` on Chromium 130.0.6723.116 on Linux Mint 22.0:

Results for current master branch:

test.html:235 INFO: time:0.004600
test.html:235 INFO: time:0.005200
test.html:235 INFO: time:0.004800
test.html:235 INFO: time:0.004900
test.html:235 INFO: time:0.004500
test.html:235 INFO: time:0.004800
test.html:235 INFO: time:0.004900
test.html:235 INFO: time:0.005000
test.html:235 INFO: time:0.004600
test.html:235 INFO: time:0.004700

Results for this PR:

test.html:235 INFO: time:0.004600
test.html:235 INFO: time:0.004700
test.html:235 INFO: time:0.004400
test.html:235 INFO: time:0.004300
test.html:235 INFO: time:0.004500
test.html:235 INFO: time:0.004800
test.html:235 INFO: time:0.004400
test.html:235 INFO: time:0.004300
test.html:235 INFO: time:0.004600
test.html:235 INFO: time:0.004800

Based on my napkin math, there was around 0.7% improvement on PLATFORM_DESKTOP_GLFW and around 5.5% improvement on PLATFORM_WEB.

[Peter0x44]

Another thing worth mentioning that I didn't change, MeasureTextEx has the variable "byteCounter" which actually counts the number of codepoints in the longest line, not bytes. Probably that should be renamed, but I didn't do it in this PR.