drm_hwcomposer: CI: Upgrade clang-* to v12

- Enabling readability-ientifier-naming tidy check does require to specify
MacroDefinitionIgnoredRegexp key, which is available only in clang-tidy-12.

- Clang-12 isn't available on ubuntu 20.10, therefore upgrade to 21.04.

- "DEBIAN_FRONTEND: noninteractive" is required to prevent ubuntu 21.04
from hanging, presumably due to waiting for the user input.

- A positive side effect of upgrading to clang-12 is new clang-tidy-12,
which exposed new issues in the code which is also fixed by this commit,
e.g:

    Failed cppcoreguidelines-narrowing-conversions check with error:
    error: narrowing conversion from 'uint32_t' (aka 'unsigned int') to 'float'

require explicit casting to pass the check, while some of such fails are caused
by incorrect variable type and fixed by changing the type to correct one.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>

README.md

@@ -16,7 +16,7 @@ A short list of contribution guidelines:
   you with formatting of your patches:
 
     ```
-    git diff | clang-format-diff-11 -p 1 -style=file
+    git diff | clang-format-diff-12 -p 1 -style=file
     ```
 
 * Hardware specific changes should be tested on relevant platforms before