This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

This removes the following deprecated features that were already showing warnings when used in Rollup 2:

• Removed the plugin context methods:
  • this.emitAsset()
  • this.emitChunk()
  • this.getAssetFileName()
  • this.getChunkFileName()
  • this.isExternal()
  • this.resolveId()
• The resolveAssetUrl hook is removed
• Rollup no longer pass an assetReferenceId or a chunkReferenceId parameter to resolveFileUrl
• The treeshake.pureExternalModules option is removed
• Emitted assets no longer have an isAsset flag in the bundle
• Rollup will no longer fix assets added directly to the bundle by adding the type: "asset" field

On the other hand, the following deprecated features will no show warnings when used:

• inlineDynamicImports as part of the input options
• preserveModules as part of the input options
• manualChunks as part of the input options
• output.preferConst
• output.dynamicImportFunction
• Using true or false for output.interop
• output.namespaceToStringTag
• Accessing this.moduleIds on the plugin context
• Accessing this.getModuleInfo(...).hasModuleSideEffects in plugins