getCompletions in a very large array literal causes tsserver to spin

[minestarks]

1. Clone https://github.com/Leaflet/Leaflet
2. Open route.js, which has a very large array declaration in it
3. Trigger completion on the close brackets (]) in the middle of the array somewhere
4. Watch tsserver eat 100% cpu for an hour

I haven't been able to attach to VS Code to take a callstack, but I have a tsserverfuzzer repro, which I believe is the same issue, and that one has the following callstack.

From stepping around in the debugger, the frame that it got stuck in seems to be findPrecedingMatchingToken - we never get out of that function.

find (tsserverlibrary.js:112323)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
find (tsserverlibrary.js:112342)
findPrecedingToken (tsserverlibrary.js:112315)
findPrecedingMatchingToken (tsserverlibrary.js:112488)
getPossibleTypeArgumentsInfo (tsserverlibrary.js:112578)
isPossiblyTypeArgumentPosition (tsserverlibrary.js:112512)
isTypeOnlyCompletion (tsserverlibrary.js:116790)
filterGlobalCompletion (tsserverlibrary.js:116761)
getGlobalCompletions (tsserverlibrary.js:116734)
tryGetGlobalSymbols (tsserverlibrary.js:116625)
getCompletionData (tsserverlibrary.js:116419)
getCompletionsAtPosition (tsserverlibrary.js:115749)
getCompletionsAtPosition (tsserverlibrary.js:144114)
Session.getCompletions (tsserverlibrary.js:154586)
...

TypeScript Version: 3.9.3, 4.1.0-dev.2020081