[clang] [clang][bytecode] Update high-level documentation (PR #202596)

[Yihan Wang via cfe-commits]

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@@ -8,12 +8,16 @@ Constant Interpreter
 Introduction
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-The constexpr interpreter aims to replace the existing tree evaluator in
+The bytecode interpreter aims to replace the existing tree evaluator in
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yronglin wrote:

nit: `tree evaluator` -> `AST traversal based evaluator`. What do you think? I have no preference.

https://github.com/llvm/llvm-project/pull/202596