Stabilize V15 Metadata (#14481)

* Update frame-metadata to latest branch

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Stabilize V15

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame-metadata

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Use frame-metadata from crates.io

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Adjust testing

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* test: Adjust frame-support metadata docs

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update primitives/metadata-ir/src/lib.rs

Co-authored-by: James Wilson <james@jsdw.me>

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Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: James Wilson <james@jsdw.me>
Co-authored-by: parity-processbot <>