Use only ASCII in source files (#10164)

Use only ASCII in source files (#10164)

Summary:
Fix existing usage of non-ASCII and add a check to prevent
future use. Added `-n` option to greps to provide line numbers.

Alternative to https://github.com/facebook/rocksdb/issues/10147

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10164

Test Plan:
used new checker to find & fix cases, manually check
db_bench output is preserved

Reviewed By: akankshamahajan15

Differential Revision: D37148792

Pulled By: pdillinger

fbshipit-source-id: 68c8b57e7ab829369540d532590bf756938855c7