Performance improvements

[DonJayamanne]

microsoft/vscode#211142

[DonJayamanne]

Though this makes things fast, I do not believe this is the root cause,
This code path is getting hit when we execute cells in a notebook,
At this points the text documsnts of the cells do not change, hence I do not think eslint should fire.

Also shouldn't the condition here be changed from
if (Languages.match(packageJsonFilter, document) || Languages.match(configFileFilter, document) || validator.check(document) !== Validate.off) {

to

if ((Languages.match(packageJsonFilter, document) || Languages.match(configFileFilter, document)) && validator.check(document) !== Validate.off) {

Perhaps I've miunserstood the code or just don't understand it, but if the cell language is Python I would have expected this path to bail early on, instead of even going into the validator.check.