Split vendored sources into their own crate.

Added

• Support building mimalloc v3 (lnslyosl)
  • Using this version breaks most of the high-level bindings in mimalloc-rich
• Support allocator-api v0.2, v0.3, and v0.4, all at once (ynxstnuk)
  • Enabled by default with mimalloc-rich/allocator-api2-all feature.

Changes

• Deprecate the MiHeap API, as it will need to be rewritten when mimalloc v3 support is added (mztqvrpx)
• Rename mimalloc-rich-sys/override feature to mimalloc-rich-sys/override-libc-malloc (zzxlwnyv)
• Split vendored sources into own crate (pvvpzosl)
  • Will reduce download time when there are multiple mimalloc versions.
  • Will reduces download time when building against a system library (not currently supported)
• Rename mimalloc-rich-sys/vendored-mimalloc to mimalloc-rich-sys/vendored (nqpsmsnn)

Associated Versions

• mimalloc@2.5.2
• mimalloc@3.5.3
• mimalloc-rich-src-v2@1.5.200
• mimalloc-rich-src-v3@1.5.300