[jrandolf]

This implements the rule from WebAssembly/component-model#756 (proposed in WebAssembly/component-model#751): the value type of a map can't transitively contain an own, borrow, future, stream or error-context. Bindings that keep only the last value of a duplicate key would otherwise have to dispose of the handles in the values they drop (bytecodealliance/wasmtime#14812).

Types already record whether they contain a borrow, for function results. This adds a bit next to it for any handle, and map validation checks it on the value type.

LLM summary of the changes

Validation (validator/component_types.rs, validator/component.rs)

• AbiInfo uses its previously unused bit 31 to record whether a type transitively contains a handle. own, borrow, future, stream and error-context set it, and records, variants, lists, maps and fixed-length lists inherit it from their fields, cases or elements, the same way as the existing borrow bit.
• Validating (map K V) fails with "map value type cannot contain a handle" when V has the bit set. Keys can't contain handles already.
• wit-parser isn't changed, so a WIT map with handles in its values still parses. Components using it fail validation.

Tests (tests/cli/component-model/map.wast)

• Handles in map values are rejected directly and when nested in option, record, list, tuple, variant and another map, including in an imported function's parameter.
• Maps can still be the payload of a stream or future.
• The test enables cm-error-context for the error-context case.

[fitzgen]

LGTM, thanks