Make `egui_plot::PlotMemory` public #8811

Job	Run time
Check wasm32 + wasm-bindgen	2m 26s
cargo-deny aarch64-apple-darwin	39s
cargo-deny aarch64-linux-android	42s
cargo-deny i686-pc-windows-gnu	41s
Format + check + test	5m 29s
cargo-deny i686-pc-windows-msvc	48s
cargo-deny i686-unknown-linux-gnu	41s
android	23s
cargo-deny wasm32-unknown-unknown	39s
cargo-deny x86_64-apple-darwin	38s
cargo-deny x86_64-pc-windows-gnu	38s
cargo-deny x86_64-pc-windows-msvc	42s
Check Windows	1m 30s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	36s
cargo-deny x86_64-unknown-redox	45s
	17m 54s

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