[clang-tidy] 'implicit cast' -> 'implicit conversion'

Summary:
This patch renames checks, check options and changes messages to use correct
term "implicit conversion" instead of "implicit cast" (which has been in use in
Clang AST since ~10 years, but it's still technically incorrect w.r.t. C++
standard).

  * performance-implicit-cast-in-loop -> performance-implicit-conversion-in-loop
  * readability-implicit-bool-cast -> readability-implicit-bool-conversion
    - readability-implicit-bool-cast.AllowConditionalIntegerCasts ->
      readability-implicit-bool-conversion.AllowIntegerConditions
    - readability-implicit-bool-cast.AllowConditionalPointerCasts ->
      readability-implicit-bool-conversion.AllowPointerConditions

Reviewers: hokein, jdennett

Reviewed By: hokein

Subscribers: mgorny, JDevlieghere, xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D36456

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@310366 91177308-0d34-0410-b5e6-96231b3b80d8
20 files changed