fix: expose ".del" function on lmdb cache

[pieh]

Description

Introduction of lmdb implementation of cache (passed to plugins) is missing .cache internal cache being exposed (as "legacy" cache does). This cause gatsby-plugin-sharp that want to use .del on that internal cache instance to crash in gatsby develop.

This PR does few things:
a) adds compat mode to lmdb cache implementation (add .cache property that is just reference to itself)
b) adds .del method on public interface (and implement it in both legacy cache and lmdb cache)
c) future proofs gatsby-plugin-sharp to use public .del if available (ideally we remove access to internal cache implementation in v4)

Related Issues

Fixes #32445

[vladar]

Probably also need to update this dummy one:

gatsby/packages/gatsby/src/utils/api-runner-node.js

Lines 229 to 244 in 9595ccb

	const getUninitializedCache = plugin => {
	const message =
	`Usage of "cache" instance in "onPreInit" API is not supported as ` +
	`this API runs before cache initialization` +
	(plugin && plugin !== `default-site-plugin` ? ` (called in ${plugin})` : ``)
	return {
	// GatsbyCache
	async get() {
	throw new Error(message)
	},
	async set() {
	throw new Error(message)
	},
	}
	}

[pieh]

Probably also need to update this dummy one:

gatsby/packages/gatsby/src/utils/api-runner-node.js

Lines 229 to 244 in 9595ccb

	const getUninitializedCache = plugin => {
	const message =
	`Usage of "cache" instance in "onPreInit" API is not supported as ` +
	`this API runs before cache initialization` +
	(plugin && plugin !== `default-site-plugin` ? ` (called in ${plugin})` : ``)
	return {
	// GatsbyCache
	async get() {
	throw new Error(message)
	},
	async set() {
	throw new Error(message)
	},
	}
	}

Added in 229a523

[vladar]

Thank you!

[LekoArts]

Fixed in gatsby-plugin-sharp@3.10.2 and gatsby@3.10.1