[javadoc] Replace < > in pre/code tags automatically

Today I noticed that JD replaces `@` in javadoc code/pre tags automatically to `@` as these needs to be escaped on save the file that is great help already :+1: .

Sadly it seem to not do the same for `<` (=`<`) and `>` (=`>`) leading to even JDT is suffering from such faulty javadoc:
- https://github.com/eclipse-jdt/eclipse.jdt.core/issues/1582

a similar issue seem to exits with `&` (=`&`)

FYI @jukzi @akurtakov