Update error messages

[xterao]

Fixed error message texts.

• In custom function checks, if doma.expr.functions is not set, show org.seasar.doma.expr.ExpressionFunctions as the reference class.
• In test data checks, specify the target directive in the message.

Also updated the SQL format settings description in the README.

[Copilot]

Pull Request Overview

This PR updates error message texts for SQL inspections, centralizes the default expression functions class name, adds a test case for empty custom functions, and clarifies auto‐indent settings in the README.

• Refined inspection error messages to mention bind or literal variable directives and updated custom‐function not‐found wording.
• Introduced EXPRESSION_FUNCTIONS_NAME constant and applied it in processor/helper.
• Added emptyImplementCustomFunctions.sql test and corresponding testEmptyImplementCustomFunctions method.
• Revised README to describe SQL formatter auto‐indent settings.

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
.../populateDirective.sql	Updated test‐data error message text
.../literalDirective.sql	Updated test‐data error message text
.../invalidTestData.sql	Updated test‐data error message text
.../conditionAndLoopDirective.sql	Updated test‐data error message text
.../commentBlock.sql	Updated test‐data error message text
.../bindVariableDirective.sql	Updated test‐data error message text
.../implementCustomFunctions.sql	Reworded custom‐function error descriptions
.../emptyImplementCustomFunctions.sql	New test data fixture for empty custom functions
ParameterDefinedTest.kt	Included new SQL in test suite and added test method
DomaToolsBundle*.properties	Localized and default messages updated to match new text
InspectionFunctionCallVisitorProcessor.kt	Defaulted missing custom‐function class to constant
ExpressionFunctionsHelper.kt	Switched hardcoded class name to constant
DomaCompileConfigUtil.kt	Introduced EXPRESSION_FUNCTIONS_NAME constant
README.md	Clarified SQL auto‐indent feature and its settings path

Comments suppressed due to low confidence (2)

src/test/testData/src/main/resources/META-INF/doma/example/dao/EmployeeSummaryDao/emptyImplementCustomFunctions.sql:2

• The alias 'e' is undefined (the FROM clause uses alias 'u'). Consider using 'u.employee_id' or renaming the table alias to 'e'.

    e.employee_id

src/test/testData/src/main/resources/META-INF/doma/example/dao/EmployeeSummaryDao/emptyImplementCustomFunctions.sql:6

• The alias 'p' is undefined in this SQL. Update it to match the declared table alias ('u') or correct the aliasing.

 WHERE p.employee_id = /* employee.employeeId */0