perf(linter/plugins): optimize getTokens() and other methods (#16188)

- Removes branching in some cases where it was used to calculate slices.
- Avoids indexing into arrays past their length.
- Renames `nodeTokens` to `tokenList`. In the first few methods
implemented, they contained tokens of the given node. Not the case for
later methods, but the misnomer stayed.
- Improves consistency in comments. Clarifies that binary searches yield
tokens before or after a certain point, they are not necessarily
_within_ the range we care about.

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Co-authored-by: overlookmotel <[email protected]>

Author: lilnasy