Build the examples generator only where it can compile

`cargo test --workspace --no-default-features` builds every target in the
workspace, examples included, and the examples generator asks for
`textprocessing::examples` -- a module behind `#[cfg(all(feature =
"chinese", feature = "korean"))]`, because it renders the whole transform
table in one pass and needs both dictionaries to do it. With the features
off the module is not there and the example does not compile, so `site
check` fails at the test step.

Nothing was wrong with either side: the module is gated because the
dictionaries are 13 MB and CI has no use for them, and the example needs
them because that is what it renders. What was missing is the line that
says so to cargo. `required-features` makes it skip the target rather than
try to build it, which is the same thing `site textprocessing-examples`
was already relying on by running with default features on.

It fails only in CI, and only in the no-default-features build, which is
why a workspace test run here has been green throughout.

Author: float3

wasm/textprocessing/Cargo.toml

@@ -38,3 +38,12 @@ pinyin_zhuyin = { version = "0.2.0", optional = true }
 
 hanja = { version = "0.1.1", optional = true }
 hangeul_conversion = { path = "hangeul_conversion", optional = true }
+
+# The generator renders the whole table in one pass, so it needs both
+# dictionaries; without this it is still built by `cargo test --workspace
+# --no-default-features`, where `textprocessing::examples` is compiled out and
+# the example cannot resolve it. CI builds the workspace exactly that way, so
+# the failure lands there and nowhere else.
+[[example]]
+name = "generate_examples"
+required-features = ["chinese", "korean"]