Only use regex lookbehind where supported

[jkillian]

What this PR does / why we need it:

Users on older versions of VSCode were hitting bugs because of lookbehinds in the camel case motion regex. This should fix the issue for those users.

Which issue(s) this PR fixes

Fixes #3522

Special notes for your reviewer:
I didn't get to test this myself on an older version of VSCode. But I think it should work?

[julie-is-late]

This is very similar to what I was testing. Looks fine. Special note that if a user is building vscodevim on an older branch that some test cases will fail, but seems fine to just say that is disallowed.

[jkillian]

Closing this since nobody has complained that they can't upgrade VSCode yet. Will keep the branch around for now though in case it becomes necessary

[CompuIves]

Hey! We're using VSCodeVIM inside CodeSandbox (https://codesandbox.io/s/new), which runs VSCode + extensions. For our VIM Mode we use VSCodeVIM (thanks for building this!).

This worked great so far, but we found out that lookbehind regexpressions are not supported in Firefox. I can imagine that this is a very unusual request but would you be open to a PR that adds the lookbehind check and disables it if it detects Firefox/Safari?

[jkillian]

reopening for consideration since it seems like there are some legit use cases

[TheJoeSchr]

is this working? I'm trying to access code-server via firefox reality and it gives me this error.

would be really cool if I could code in VR and so far this is the only roadblock :(

anyways thanks for building VSCodeVim, it's really fine!

[shritesh]

This was removed again in 1d273eb#diff-4eb584e50b8970dfd9f200f6d934f418

[DAddYE]

This was removed again in 1d273eb#diff-4eb584e50b8970dfd9f200f6d934f418

I'm using vscode 1.46.1 through code-server on ipad and I'm getting:

Activating extension 'vscodevim.vim' failed: Invalid regular expression: invalid group specifier name.
_logMessageInConsole — abstractExtensionService.ts:396
_logOrShowMessage — abstractExtensionService.ts:410
(anonymous function) — mainThreadExtensionService.ts:70
asyncFunctionResume
_invokeHandler — rpcProtocol.ts:387
_receiveRequest — rpcProtocol.ts:303
_receiveOneMessage — rpcProtocol.ts:230
fire — event.ts:587
(anonymous function) — webWorkerExtensionHostStarter.ts:70
console.ts:137

[J-Fields]

Ah, I hadn't considered us running in the browser when I removed that. I'll fix it momentarily.

[DAddYE]

Ah, I hadn't considered us running in the browser when I removed that. I'll fix it momentarily.

Thanks so much guys!

[DAddYE]

Ah, I hadn't considered us running in the browser when I removed that. I'll fix it momentarily.

Seems is still not working, I tested from master and still has errors with some grouped regex.
I'll try in the next few days to see if I can profile/debug the extension, because currently the inspector isn't super helpful.

[J-Fields]

@DAddYE Just created #5072, I'll try to resolve when I have a chance

[Immortalin]

@J-Fields any luck?