[release][Dont Squash] Update version to 0.19.0 and 0.20.0.dev on main branch

[ysh329]

Make version modification twice as two commits:

• First, to v0.19.0 on main branch.
• Second, to v0.20.dev0 on main branch in one PR.

NOTE: Don't squash when merge.

cc: @Hzfengsy @vinx13

[Hzfengsy]

@tvm-bot rerun

[ysh329]

Hi @Hzfengsy, It seems that CI failed during the build period. Can you roughly tell what the reason is?

[Hzfengsy]

@tqchen @yongwww are updating CI machines. would be great if you guys could help fix it :)

[yongwww]

hi @ysh329, the ARM build issue is due to memory limits. We're looking into upgrading the instance type or adding swap space. Will update you on our progress.

[ysh329]

hi @ysh329, the ARM build issue is due to memory limits. We're looking into upgrading the instance type or adding swap space. Will update you on our progress.

Thanks a lot.

[yongwww]

@tvm-bot rerun