Auto merge of #98463 - mystor:expand_expr_bool, r=eddyb

Auto merge of #98463 - mystor:expand_expr_bool, r=eddyb

proc_macro: Fix expand_expr expansion of bool literals

Previously, the expand_expr method would expand bool literals as a
`Literal` token containing a `LitKind::Bool`, rather than as an `Ident`.
This is not a valid token, and the `LitKind::Bool` case needs to be
handled seperately.

Tests were added to more deeply compare the streams in the expand-expr
test suite to catch mistakes like this in the future.