RFR: 8377895: Create sizeof_auto, to reduce narrowing conversions

[Leo Korinth]

`sizeof_auto` is created so that we can reduce the amount of casting and thus make the code more type safe. The normal `sizeof` will return a `size_t` although the size of most stuff can be represented in a `uint8_t`. `sizeof_auto` will return the size in an as small unsigned type as is possible. The result is that expressions that uses `sizeof_auto` can convert to most integral types, and no explicit narrowing cast will be needed.

The change in `cpCache.hpp` is an example where we would get an implicit narrowing warning (if we had those enabled) using normal `sizeof`, but where `sizeof_auto` will not make the expression a `size_t` .

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Commit messages:
 - 8377895: Create sizeof_auto, to reduce narrowing conversions

Changes: https://git.openjdk.org/jdk/pull/29716/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29716&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377895
  Stats: 53 lines in 3 files changed: 52 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29716.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29716/head:pull/29716

PR: https://git.openjdk.org/jdk/pull/29716