meson: switch to 0.57.0

- The intent behind this commit is switch meson version to 0.57.0
  and switch C++ version to 20.

- Also, Because the meson call `source_root` is deprecated
  since 0.56.0, switch to `project_source_root` and is the correct
  replacement for the deprecated `source_root`.

Tested: built ledManager repo successfully and worked.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I5ef0569df0be22470104aea493812efa24516639
5 files changed