rename DEFAULT_PAGE_SIZE to PAGE_SIZE

[Carlyle-Foster]

to reflect that it's often not just a default

[Kelimion]

And we have another hardcoded one in core:mem/alloc.odin.

DEFAULT_PAGE_SIZE ::
	64 * 1024 when ODIN_ARCH == .wasm32 || ODIN_ARCH == .wasm64p32 else
	16 * 1024 when ODIN_OS == .Darwin && ODIN_ARCH == .arm64 else
	4 * 1024

@gingerBill may want to consider whether and how to consolidate these.

[Carlyle-Foster]

And we have another hardcoded one in core:mem/alloc.odin.

DEFAULT_PAGE_SIZE ::
	64 * 1024 when ODIN_ARCH == .wasm32 || ODIN_ARCH == .wasm64p32 else
	16 * 1024 when ODIN_OS == .Darwin && ODIN_ARCH == .arm64 else
	4 * 1024

@gingerBill may want to consider whether and how to consolidate these.

my latest commits are a draft of consolidation