Add open-source 'basic' cache provider and revamp licensing documentation (#930)

## Summary

- **New `basic` cache provider**: Adds an open-source (MIT-licensed)
caching implementation built on `@actions/cache` as an alternative to
the proprietary Enhanced Caching. Users can opt in with `cache-provider:
basic` on both `setup-gradle` and `dependency-submission` actions.
- **Revamped licensing & distribution docs**: Replaces the verbose
licensing notice block (previously shown in README, docs, and logs) with
a friendlier callout and a new dedicated
[DISTRIBUTION.md](./DISTRIBUTION.md) covering component licensing, usage
tiers, data privacy ("Safe Harbor"), and opt-out instructions.
- **Improved messaging**: Enhanced Caching and Basic Caching each
display concise, informative log messages and job summary notes instead
of the previous wall-of-text license warning.
- **New integration tests**: Adds `integ-test-basic-cache-provider.yml`
workflow that seeds and verifies the basic cache provider across
platforms, plus unit tests for `BasicCacheService` and `getCacheService`
selection logic.
- **CI workflow reorganization**: Dependency-submission integration
tests extracted into their own reusable suite
(`suite-integ-test-dependency-submission.yml`); sample project tests
moved into the caching suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sources/src/cache-service-basic.ts

@@ -0,0 +1,85 @@
+import * as cache from '@actions/cache'
+import * as core from '@actions/core'
+import * as glob from '@actions/glob'
+import * as path from 'path'
+
+import {BuildResult} from './build-results'
+import {CacheOptions, CacheService} from './cache-service'
+
+const PRIMARY_KEY_STATE = 'BASIC_CACHE_PRIMARY_KEY'
+const RESTORED_KEY_STATE = 'BASIC_CACHE_RESTORED_KEY'
+const CACHE_KEY_PREFIX = 'setup-java'
+
+const GRADLE_BUILD_FILE_PATTERNS = [
+    '**/*.gradle*',
+    '**/gradle-wrapper.properties',
+    'buildSrc/**/Versions.kt',
+    'buildSrc/**/Dependencies.kt',
+    'gradle/*.versions.toml',
+    '**/versions.properties'
+]
+
+export class BasicCacheService implements CacheService {
+    async restore(gradleUserHome: string, _cacheOptions: CacheOptions): Promise<void> {
+        const cachePaths = getCachePaths(gradleUserHome)
+        const primaryKey = await computeCacheKey()
+        core.saveState(PRIMARY_KEY_STATE, primaryKey)
+
+        // No "restoreKeys" is set, to start with a clear cache after dependency update
+        // See https://github.com/actions/setup-java/issues/269
+        try {
+            const restoredKey = await cache.restoreCache(cachePaths, primaryKey)
+            if (restoredKey) {
+                core.saveState(RESTORED_KEY_STATE, restoredKey)
+                core.info(`Basic caching restored from cache key: ${restoredKey}`)
+            } else {
+                core.info('Basic caching did not find an entry to restore. Will start with empty state.')
+            }
+        } catch (error) {
+            core.warning(`Basic caching failed to restore from cache: ${error}`)
+        }
+    }
+
+    async save(gradleUserHome: string, _buildResults: BuildResult[], cacheOptions: CacheOptions): Promise<string> {
+        if (cacheOptions.readOnly) {
+            const restoredKey = core.getState(RESTORED_KEY_STATE)
+            if (restoredKey) {
+                return `Basic caching was read-only. Restored from cache key \`${restoredKey}\`.`
+            }
+            return 'Basic caching was read-only. No cache entry was found to restore.'
+        }
+
+        const primaryKey = core.getState(PRIMARY_KEY_STATE)
+        const restoredKey = core.getState(RESTORED_KEY_STATE)
+
+        if (restoredKey === primaryKey) {
+            core.info(`Basic caching restored entry with key \`${primaryKey}\`. Save was skipped.`)
+            return `Basic caching restored entry with key \`${primaryKey}\`. Save was skipped.`
+        }
+
+        const cachePaths = getCachePaths(gradleUserHome)
+
+        try {
+            await cache.saveCache(cachePaths, primaryKey)
+            core.info(`Basic caching saved entry with key: ${primaryKey}`)
+            return `Basic caching saved entry with key \`${primaryKey}\`.`
+        } catch (error) {
+            core.warning(`Basic caching failed to save entry with key \`${primaryKey}\`: ${error}`)
+            return `Basic caching save failed: ${error}`
+        }
+    }
+}
+
+function getCachePaths(gradleUserHome: string): string[] {
+    return [path.join(gradleUserHome, 'caches'), path.join(gradleUserHome, 'wrapper')]
+}
+
+async function computeCacheKey(): Promise<string> {
+    const fileHash = await glob.hashFiles(GRADLE_BUILD_FILE_PATTERNS.join('\n'))
+    if (!fileHash) {
+        throw new Error(
+            `No file in ${process.cwd()} matched to [${GRADLE_BUILD_FILE_PATTERNS}], make sure you have checked out the target repository`
+        )
+    }
+    return `${CACHE_KEY_PREFIX}-${process.env['RUNNER_OS']}-${process.arch}-gradle-${fileHash}`
+}