Move caching into setup-java, correct READMEs

New setup-java version can cache local Maven repository for us, so
make it so.

Make READMEs go back to saying "mvn install" instead of "mvn package"
because I forgot a single pom file needs to be installed into the
local Maven repository for the build to work (then you can say "mvn
package" for everything else).

.github/workflows/integration.yml

@@ -8,7 +8,7 @@ on:
     types: [opened, synchronize, reopened]
   workflow_dispatch:
 
-# Runs a build job as a check:
+# Runs a build job as a CI check:
 # - Builds VERDICT source & runs unit tests
 
 jobs:
@@ -33,13 +33,7 @@ jobs:
       with:
         distribution: ${{ matrix.distribution }}
         java-version: ${{ matrix.java-version }}
-
-    - name: Set up Maven cache
-      uses: actions/[email protected]
-      with:
-        path: ~/.m2/repository
-        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
-        restore-keys: ${{ runner.os }}-maven-
+        cache: maven
 
     - name: Build VERDICT source
       run: |

.github/workflows/main.yml

@@ -60,14 +60,7 @@ jobs:
       with:
         distribution: ${{ matrix.distribution }}
         java-version: ${{ matrix.java-version }}
-
-    - name: Set up Maven cache
-      if: runner.os == 'Linux'
-      uses: actions/[email protected]
-      with:
-        path: ~/.m2/repository
-        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
-        restore-keys: ${{ runner.os }}-maven-
+        cache: maven
 
     - name: Build VERDICT source
       if: runner.os == 'Linux'

.github/workflows/release.yml

@@ -105,13 +105,7 @@ jobs:
       with:
         distribution: ${{ matrix.distribution }}
         java-version: ${{ matrix.java-version }}
-
-    - name: Set up Maven cache
-      uses: actions/[email protected]
-      with:
-        path: ~/.m2/repository
-        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
-        restore-keys: ${{ runner.os }}-maven-
+        cache: maven
 
     - name: Build VERDICT source
       run: |

tools/README.md

@@ -24,11 +24,13 @@ subdirectories:
 Please read the development instructions in these subdirectories'
 README.md files for further details.  Note that you can descend into
 each subdirectory and build it with Maven separately or you can build
-all three subdirectories from this location with these Maven commands:
+all three subdirectories from this location with these two commands,
+making sure to call the clean and install goals separately (not in the
+same Maven command line):
 
 ```shell
 mvn clean
-mvn package -Dtycho.localArtifacts=ignore
+mvn install -Dtycho.localArtifacts=ignore
 ```
 
 ## Install our VERDICT plugin

tools/verdict-back-ends/README.md

@@ -103,8 +103,8 @@ in that mirrorOf section before your build will finish successfully.
 
 ## Build the Java back-end programs
 
-To build the Java program sources on your system, simply run the
-following Maven command:
+To build the Java program sources on your system, run the following
+command in this directory:
 
 `mvn clean install`
 

tools/verdict/README.md

@@ -87,12 +87,12 @@ This directory and its subdirectories have pom.xml files which will
 allow you to build our VERDICT plugin sources with Maven and Eclipse
 Tycho.  We recommend that you build our VERDICT plugin sources with
 Maven from the command line in this directory or the directory above,
-making sure to call the clean and package goals separately (not in the
+making sure to call the clean and install goals separately (not in the
 same Maven command line):
 
 ```shell
 mvn clean
-mvn package -Dtycho.localArtifacts=ignore
+mvn install -Dtycho.localArtifacts=ignore
 ```
 
 Using the `-Dtycho.localArtifacts=ignore` argument may prevent some