Improve render performance (#511)

Massive improvement of render performance by:
- replacing the codimd-line-marker with an in-memory map
- an observation of the changed markdown code to identify changed lines
- a unique react-key calculation

src/components/markdown-renderer/replace-components/pdf/pdf-replacer.tsx

@@ -1,19 +1,19 @@
 import { DomElement } from 'domhandler'
 import React from 'react'
 import { getAttributesFromCodiMdTag } from '../codi-md-tag-utils'
-import { ComponentReplacer, SubNodeConverter } from '../ComponentReplacer'
+import { ComponentReplacer } from '../ComponentReplacer'
 import { PdfFrame } from './pdf-frame'
 
-export class PdfReplacer implements ComponentReplacer {
+export class PdfReplacer extends ComponentReplacer {
   private counterMap: Map<string, number> = new Map<string, number>()
 
-  getReplacement (node: DomElement, index: number, subNodeConverter: SubNodeConverter): React.ReactElement | undefined {
+  public getReplacement (node: DomElement, index: number): React.ReactElement | undefined {
     const attributes = getAttributesFromCodiMdTag(node, 'pdf')
     if (attributes && attributes.url) {
       const pdfUrl = attributes.url
       const count = (this.counterMap.get(pdfUrl) || 0) + 1
       this.counterMap.set(pdfUrl, count)
-      return <PdfFrame key={`pdf_${pdfUrl}_${count}`} url={pdfUrl}/>
+      return <PdfFrame key={index} url={pdfUrl}/>
     }
   }
 }