RFR: 7903981: Support easy way to use current class name for test actions [v6]

[Christian Stein]

> Please review this change to allow an easier way to use current class name for test actions.
> 
> Test authors usually specify the name of a test class to be run by `jtreg` 1:1 in a `@run` action directive. This PR introduces the new test property `test.main.class` and tries to initialize it with the fully-qualified class name of the test class. It is composed of the package name and the truncated file name of `.java` source file passed to `jtreg`: `SomeTest.java` becomes `SomeTest`
> 
> Example for `Test.java` in the unnamed package:
> - `@run main Test` - `@run main ${test.main.class}`
> 
> Example for `Test.java` declaring `package p;`:
> - `@run main p.Test` - `@run main ${test.main.class}`
> 
> See also: [CODETOOLS-7902352: Support use of ${property.name} in action args](https://bugs.openjdk.org/browse/CODETOOLS-7902352)

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Use canonical expression for expecting non-zero result

-------------

Changes:
  - all: https://git.openjdk.org/jtreg/pull/257/files
  - new: https://git.openjdk.org/jtreg/pull/257/files/a2f950c0..fee34761

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=257&range=05
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=257&range=04-05

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jtreg/pull/257.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/257/head:pull/257

PR: https://git.openjdk.org/jtreg/pull/257