Feature: Add version/build identifier to LexicalEditor

[etrepum]

It's useful when debugging, and will presumably be useful for devtools, if details of the lexical build are present in the editor. The __DEV__ checks could also use this introspection capability to help people debug the dreaded LexicalComposerContext.useLexicalComposerContext: cannot find a LexicalComposerContext when there is a bundler configuration issue causing multiple builds of lexical to be present. Possibly something like '0.15.0-cjs-dev' or '0.15.0-esm-prod'. I don't have any strong opinions on the format of the version or build string that is included.

It could be present on the editor as a static, so it would be accessible with lexicalEditor.constructor.BUILD_IDENTIFIER or whatever naming convention is decided upon.

I think the three important things are:

• Version
• CJS/ESM
• prod/dev

It wouldn't prevent all possible problems (e.g. a dependency could bundle the same build of lexical not as an external) but I think it would be helpful and have negligible impact to build size or runtime.