fix(grammar): The TSG grammar for Java does not handle the static_initializer node

[drestrepom]

• Add the static_initializer node for the Java grammar, this node may contain multiple statements, such as initializing variables or executing functions

[drestrepom]

Here, a demonstration of what happens when that node is not handled

test/decl/static_initializer.java: failed to build stack graph
    0: Error executing statement edge @class_body.defs -> @declaration.defs at (225, 3)
       src/stack-graphs.tsg:225:3:
       225 |   edge @class_body.defs -> @declaration.defs
           |   ^
       in stanza
       src/stack-graphs.tsg:224:1:
       224 | (class_body (_)@declaration)@class_body {
           | ^
       matching (class_body) node
       test/decl/static_initializer.java:1:17:
       1 | class TestClass {
         |                 ^
    1: Evaluating edge sink
    2: Undefined scoped variable [syntax node static_initializer (2, 3)].defs

Error: Failed to build graph for test/decl/static_initializer.java
error: test failed, to rerun pass `--test test`

This is an example of using this node in a concurred repository

https://github.com/OWASP-Benchmark/BenchmarkJava/blob/master/src/main/java/org/owasp/benchmark/helpers/DatabaseHelper.java#L46