OPENDJ-1308 Migrate schema support

Preparation work for removing org.opends.server.api.MatchingRule.normalizeAssertionValue().


Assertion.java:
In matches(), renamed attributeValue parameter to normalizedAttributeValue.

MatchingRuleImpl.java:
In getAssertion(), renamed value parameter to assertionValue.
Fixed javadocs.

AbstractApproximateMatchingRuleImpl.java, AbstractEqualityMatchingRuleImpl.java: ADDED
Made the relevant approximate and equality matching rule classes subclass these new ones.

AbstractMatchingRuleImpl.java:
In getAssertion(), returned UNDEFINED_ASSERTION.
Extracted method trimConsecutiveSpaces() here from several places in the code.

WordEqualityMatchingRuleImpl.java: REMOVED
Implementation was the same as KeywordEqualityMatchingRuleImpl so reused that class instead + updated CoreSchemaImpl.

KeywordEqualityMatchingRuleImpl.java:
Extracted method isAcceptable().
Removed useless calls to String.intern() on String literals.

IntegerFirstComponentEqualityMatchingRuleImpl.java:
In getAssertion(), used DefaultEqualityAssertion instead of custom built Assertion.

EnumSyntaxTestCase.java:
Made the code more readable.

*.java:
Simplified code by using ConditionResult.valueOf().