Uses `clang::Parser::ParseConstantExpression()` to parse the macro
replacement tokens, added as a token stream to the preprocessor. This
extends the support from simple object-like macros with a single
replacement token, to multiple tokens like unary operators, binary
operators, casting, nested macros etc.
The support is still limited to macros that are evaluated to an integer
constant. More types to be added as a follow-up.
Part of #6303