Expand APFS container using free space located before the container within macOS
I copy the contents of the container to a new disk / volume and then evaluate if it's faster to erase the entire drive or I want to merge / rearrange things.
The short answer is the tools are designed to have one container for the entire storage so you can move date between volumes without running into ordering issues. One container per drive is how I run boot volumes to avoid painting myself into a corner like you have done here.
The long answer is use volumes inside a container so you're working on a synthesized disk as opposed to a physical disk.
/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +499.9 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume ⁨macOS - Data⁩            327.0 GB   disk1s1
   2:                APFS Volume ⁨Preboot⁩                 255.2 MB   disk1s2
   3:                APFS Volume ⁨Recovery⁩                664.6 MB   disk1s3
   4:                APFS Volume ⁨VM⁩                      2.1 GB     disk1s4
   5:                APFS Volume ⁨macOS⁩                   15.2 GB    disk1s5
   6:              APFS Snapshot ⁨com.apple.os.update-...⁩ 15.2 GB    disk1s5s1

So, in your case, here is what a machine might look like as you prepare to upgrade to Big Sur where you can maintain a Catalina / Mojave and Big Sur beta Volume alongside the Big Sur shipping version when it's time to upgrade Macintosh HD to Big Sur.
me@dev ~ % diskutil list        
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.1 GB   disk0s2
   3:       Apple_KernelCoreDump                         655.4 MB   disk0s3

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.1 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD - Data     71.9 GB    disk1s1
   2:                APFS Volume Preboot                 81.2 MB    disk1s2
   3:                APFS Volume Recovery                525.8 MB   disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4
   5:                APFS Volume bitbucket               99.7 GB    disk1s5
   6:                APFS Volume Macintosh HD            11.5 GB    disk1s6
   7:                APFS Volume Big Sur                 761.9 KB   disk1s7
   8:                APFS Volume Mojave                  761.9 KB   disk1s8
   9:                APFS Volume Catalina                761.9 KB   disk1s9

Also, now that I said you can't do it - can you shrink the files on disk0s3 so that it fits in disk0s2 / move the data, then delete disk0s3 and grow disk0s2 to consume the now free space at the end of the physical disk?