[#12385] feat(api): Add structured Metric View Java API

[mchades]

What changes were proposed in this pull request?

Add the public Java API for structured Metric Views described in #12360:

• Introduce MetricRepresentation and OSI-compatible semantic model types.
• Add string-based MetricDialects constants and immutable builders.
• Add View#metricRepresentation() and ViewCatalog#createMetricView().
• Add API unit tests for the new types and helpers.

Why are the changes needed?

Gravitino needs a typed public contract for representing Metric Views through the existing View lifecycle. This PR establishes the Java API layer; REST, persistence, clients, server-side validation, and query execution are outside its scope.

Fix: #12385

Does this PR introduce any user-facing change?

Yes. It adds new @Unstable public Java APIs for creating and reading structured Metric Views.

How was this patch tested?

• ./gradlew :api:test :api:javadoc :api:spotlessCheck

[github-actions]

Code Coverage Report

Overall Project	68.32% +0.01%	🟢
Files changed	71.11%	🟢

Module	Coverage
aliyun	1.72%	🔴
api	51.36% +2.0%	🟢
authorization-common	85.96%	🟢
aws	42.04%	🟢
azure	2.47%	🔴
catalog-common	9.92%	🔴
catalog-fileset	79.74%	🟢
catalog-glue	68.95%	🟢
catalog-hive	79.4%	🟢
catalog-jdbc-common	45.7%	🟢
catalog-jdbc-doris	81.8%	🟢
catalog-jdbc-mysql	79.33%	🟢
catalog-jdbc-postgresql	83.39%	🟢
catalog-jdbc-starrocks	79.16%	🟢
catalog-kafka	77.01%	🟢
catalog-lakehouse-generic	59.18%	🟢
catalog-lakehouse-hudi	79.1%	🟢
catalog-lakehouse-iceberg	85.86%	🟢
catalog-lakehouse-paimon	84.23%	🟢
catalog-model	77.72%	🟢
cli	44.48%	🟢
client-java	78.27%	🟢
common	52.57%	🟢
core	83.2%	🟢
filesystem-hadoop3	77.28%	🟢
flink	0.0%	🔴
flink-common	48.68%	🟢
flink-runtime	0.0%	🔴
gcp	14.12%	🔴
hadoop-auth	68.0%	🟢
hadoop-common	12.7%	🔴
hive-metastore-common	53.4%	🟢
iceberg-common	64.75%	🟢
iceberg-rest-server	75.1%	🟢
idp-basic	86.02%	🟢
integration-test-common	0.0%	🔴
jobs	62.92%	🟢
lance-common	31.75%	🔴
lance-rest-server	63.47%	🟢
lineage	53.02%	🟢
optimizer	83.24%	🟢
optimizer-api	21.95%	🔴
server	85.88%	🟢
server-common	76.45%	🟢
spark	28.57%	🔴
spark-common	45.89%	🟢
tencent	69.84%	🟢
trino-connector	40.29%	🟢

Files

Module	File	Coverage
api	SemanticModel.java	96.08%	🟢
	SemanticModelUtils.java	95.24%	🟢
	MetricRepresentation.java	88.89%	🟢
	View.java	84.21%	🟢
	Dataset.java	77.97%	🟢
	AIContext.java	74.47%	🟢
	Field.java	71.43%	🟢
	CustomExtension.java	63.64%	🟢
	DialectExpression.java	63.64%	🟢
	Relationship.java	58.18%	🔴
	Metric.java	51.28%	🔴
	Dimension.java	50.0%	🔴
	Expression.java	50.0%	🔴
	ViewCatalog.java	22.22%	🔴
	Representation.java	0.0%	🔴
	MetricDialects.java	0.0%	🔴