refactor: refactoring matchers.SpatialMatcher

[vvatanabe]

refactoring matchers.SpatialMatcher:

• Extracted part of the process within the execute function into a separate function.
• Applied google-java-format.
• Removed the redundant extend function from BaseMatcher.
• Made the regular expression object shiftedRx static to reduce the number of times it's created.
• Changed the default ADJACENTS to private static final to minimize the number of instances created.
• By storing the result of String.valueOf(charAt) in a variable and reusing it, the duplication of operations was reduced.

[coveralls]

coverage: 92.378% (+0.03%) from 92.353% when pulling a52747dc5bc4ee02ccc716e55098b4b4a66dd0bc on refactoring-SpatialMatcher into 181cb403962d033c64a67c0a250bdf11355ba840 on master.