rsdlEditor: build parser from lezer grammar

[ralfhandl]

The lezer-rsdl.grammar needs to be compiled into JS, and the output seems to have been manually copied into lang.js, or this file had once been generated and then manually modified. Both approaches aren't sustainable:

• reverse-engineer how lang.js had originally been created
• extract the generated parts from lang.js and import them
• rebuild the lezer parser as part of the build script
  • add npm script similar to lezer-generator ./src/lang-rsdl/lezer-rsdl.grammar -o src/lang-rsdl/lang.js --noTerms --export rsdl
  • call it within build script before rollup