* build.zig: let user decide how to set build mode
This should delegate the responsibility of calling `standardReleaseOptions` and setting the build mode of the `*LibExeObjStep` step to the caller, especially since this might not be the process by which one wants to determine the build mode.
Also changes hides `getSrcDir` to enforce usage of `srcdir`, and asserts that the file is in fact inside a directory.
* build.zig: set root_src param to `null`
Supplying the header file as the root source here appears to cause a linker warning of the form:
```
LLD Link... warning(link): unexpected LLD stderr:
ld.lld: warning: {build_root}/zig-cache/o/{hash}/libraylib.a: archive member '{build_root}/zig-cache/o/{hash}/raylib.o' is neither ET_REL nor LLVM bitcode
```
Passing `null` instead fixes it.
* parser: Fail gracefully if a nonexistent file is passed on the command line
Before, if a nonexistent file was passed to LoadFileText(), it would
return NULL, and the parser would happily dereference it.
* parser: Refactor Makefile and update the path to easings.h (now reasings.h)
Before, the `make all` target would simply segfault, see 0a679d79
Now, if a file in the `make all` target doesn't exist, make will write
an error.
Individual API files can be generated likeso, provided the header file
the target depends on exists:
FORMAT=JSON EXTENSION=json make raygui_api.json
In order for the `make all` target to succeed, raygui.h, physac.h and
rmem.h need to be added to the correct directory.
* Use RL_QUADS/RL_TRIANGLES for single-pixel drawing
Addresses problem mentioned in
https://github.com/raysan5/raylib/issues/2744#issuecomment-1273568263
(in short: when drawing pixels using DrawPixel{,V} in camera mode,
upscaled pixel becomes a line instead of bigger pixel)
* [rtextures] Fixed scaling down in ImageTextEx
Closes#2755