winbuild: Refactor dependency versions into constants

[hugovk]

Changes proposed in this pull request:

• Move global __main__ calls into main() to avoid shadowing variables
• Refactor version numbers into constants to reduce duplication and make updating easier

See also the last commit, I first put them as separate constants like:

BROTLI_VERSION = "1.1.0"
FREETYPE_VERSION = "2.13.2"
...

I then refactored that into a single dict:

V = {
    "BROTLI": "1.1.0",
    "FREETYPE": "2.13.2",
    ....

So we can refer to them like V['BROTLI'] instead of BROTLI_VERSION, but I'm not sure which I prefer.

Thoughts?

cc @nulano

[nulano]

Looks good.

Two suggestions:

• Do we also want V['libimagequant'] for consistency?
• I would also include SF_PROJECTS in the format strings now that it's not the only variable. IIRC it was done with a plus operator because it was the same length, but now it saves one character :).

[hugovk]

Two suggestions:

• Do we also want V['libimagequant'] for consistency?

Yes, but let's do it when we're no longer pointing to a Git hash:

Pillow/winbuild/build_prepare.py

Lines 324 to 344 in 1b7bcfb

	"libimagequant": {
	# commit: Merge branch 'master' into msvc (matches 2.17.0 tag)
	"url": "https://github.com/ImageOptim/libimagequant/archive/e4c1334be0eff290af5e2b4155057c2953a313ab.zip",
	"filename": "libimagequant-e4c1334be0eff290af5e2b4155057c2953a313ab.zip",
	"dir": "libimagequant-e4c1334be0eff290af5e2b4155057c2953a313ab",
	"license": "COPYRIGHT",
	"patch": {
	"CMakeLists.txt": {
	"if(OPENMP_FOUND)": "if(false)",
	"install": "#install",
	# libimagequant does not detect MSVC x86_arm64 cross-compiler correctly
	"if(${{CMAKE_SYSTEM_PROCESSOR}} STREQUAL ARM64)": "if({architecture} STREQUAL ARM64)", # noqa: E501
	}
	},
	"build": [
	*cmds_cmake("imagequant_a"),
	cmd_copy("imagequant_a.lib", "imagequant.lib"),
	],
	"headers": [r"*.h"],
	"libs": [r"imagequant.lib"],
	},

• I would also include SF_PROJECTS in the format strings now that it's not the only variable. IIRC it was done with a plus operator because it was the same length, but now it saves one character :).

Good idea, suggestions applied!

[hugovk]

I've added a couple more commits to silence IDE (PyCharm) squiggly warnings.