message: Fix Support preview for $$...$$
diff: @@ -284,13 +284,13 @@ export class HoverProvider implements vscode.HoverProvider {
  }
  private stripTeX(tex: string) : string {
  - if (tex.startsWith('$') && tex.endsWith('$')) {
  + if (tex.startsWith('$$') && tex.endsWith('$$')) {
  + tex = tex.slice(2, tex.length - 2)
  + } else if (tex.startsWith('$') && tex.endsWith('$')) {
  tex = tex.slice(1, tex.length - 1)
  - }
  - if (tex.startsWith('\\(') && tex.endsWith('\\)')) {
  + } else if (tex.startsWith('\\(') && tex.endsWith('\\)')) {
  tex = tex.slice(2, tex.length - 2)
  - }
  - if (tex.startsWith('\\[') && tex.endsWith('\\]')) {
  + } else if (tex.startsWith('\\[') && tex.endsWith('\\]')) {
  tex = tex.slice(2, tex.length - 2)
  }
  return tex
  @@ -402,7 +402,7 @@ export class HoverProvider implements vscode.HoverProvider {
  const envname = this.getFirstRmemberedSubstring(document.getText(r), envBeginPat)
  return this.findHoverOnEnv(document, envname, r.start)
  }
  - const parenBeginPat = /(\\\[|\\\()/
  + const parenBeginPat = /(\\\[|\\\(|\$\$)/
  r = document.getWordRangeAtPosition(position, parenBeginPat)
  if (r) {
  const paren = this.getFirstRmemberedSubstring(document.getText(r), parenBeginPat)
  @@ -513,7 +513,7 @@ export class HoverProvider implements vscode.HoverProvider {
  // ^
  // startPos
  private findHoverOnParen(document: vscode.TextDocument | TextDocumentLike, envname: string, startPos: vscode.Position) : TexMathEnv | undefined {
  - const pattern = envname === '\\[' ? /\\\]/ : /\\\)/
  + const pattern = envname === '\\[' ? /\\\]/ : envname === '\\(' ? /\\\)/ : /\$\$/
  const startPos1 = new vscode.Position(startPos.line, startPos.character + envname.length)
  const endPos = this.findEndPair(document, pattern, startPos1)
  if ( endPos ) {
  