[clang][www] Documentation revision and proof read for features.html (#156620)
This is mostly just a small proof read for the
https://clang.llvm.org/features.html documentation page.
The changes include some typo fixes and suggestions I've found would be
useful.
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Co-authored-by: Lucas Mellone <lucasmellone@MAC-MINI.station>
Co-authored-by: lknknm <sxswt@protonmail.com>