Unify String Params' case-insensitivity in ML

For now, there are three ways to deal with case-insensitivity in ML:

1, support case-insensitivity, e.g. LogisticRegression;

2, support case-insensitivity, but with getter returning the lower case value (not the value passed to setter), e.g. ALS,DecisionTreeClassifier;

3, do not support case-insensitivity, e.g. NaiveBayes

This situation result in confusion in usage. 

I think we should choose the first way to support case-insensitivity of all non-columnName string params, including:

• LogisticRegression: family
• MultilayerPerceptronClassifier: solver
• NaiveBayes: modelType
• DecisionTreeClassifier: impurity
• RandomForestClassifier: featureSubsetStrategy, impurity
• GBTClassifier: featureSubsetStrategy, impurity, lossType
• {{}}
• LinearRegression: solver, loss
• GeneralizedLinearRegression: family, link, solver
• DecisionTreeRegressor: impurity
• RandomForestRegressor: featureSubsetStrategy, impurity
• GBTRegressor: featureSubsetStrategy, impurity, lossType
• {{}}
• {{KMeans: }}initMode
• LDA: optimizer
• PowerIterationClustering{{: }}initMode
• ALS: coldStartStrategy, intermediateStorageLevel, finalStorageLevel
• Bucketizer: handleInvalid
• ChiSqSelector: selectorType
• Imputer: strategy
• QuantileDiscretizer: handleInvalid
• RFormula: handleInvalid, stringIndexerOrderType
• StringIndexer: handleInvalid, stringOrderType
• VectorAssembler: handleInvalid
• VectorIndexer: handleInvalid
• VectorSizeHint: handleInvalid
• OneHotEncoderEstimator: handleInvalid (this will be let alone until the breaking change)
• BinaryClassificationEvaluator: metricName
• MulticlassClassificationEvaluator: metricName
• RegressionEvaluator: metricName
• ClusteringEvaluator: metricName, distanceMeasure

To to this:

• methods lowerCaseInArray and upperCaseInArray are created in ParamValidators to check case-insensitivity;
• methods  {{$$(param: Param[String])}} and %%(param: Param[String]) are created in trait Params to lower/upper the param value conveniently, and this can minimize the modifications in existing codes, since in many cases we only need to change $(param) to $${param};
• in SharedParamsCodeGen, handleInvalid and distanceMeasure are updated to use  lowerCaseInArray