RFR: 8297071: Provide gradle "TEST_ONLY" flag to completely suppress building the sdk and shims [v4]

[Ambarish Rapte]

> Add `TEST_ONLY` flag to gradle with default value as false.
> Add new task named `shims`, This task depends on all shim tasks from all projects. Hence it will build all shim classes.
> 
> If TEST_ONLY is set to true, the all non test tasks get disabled. When running a test task, this flag would reduce time in checking if all non test tasks are up to date.
> How to use:
> 1. Following command would fail in a clean repo, 
>   > gradle -PTEST_ONLY=true :base:test
> 2. The sdk and shims task must have been executed before running any test
>   > gradle sdk shims
>   > gradle -PTEST_ONLY=true :base:test
> 3. Setting this flag to true with non test task would result in no task being run.
>   > gradle -PTEST_ONLY=true sdk  -> It will not build sdk task
> 
> TIP: use `--dry-run` option of gradle for speeding up testing the effect of this PR.

Ambarish Rapte has updated the pull request incrementally with one additional commit since the last revision:

  address review comments

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1117/files
  - new: https://git.openjdk.org/jfx/pull/1117/files/980000e7..908e8fcb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1117&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1117&range=02-03

  Stats: 9 lines in 2 files changed: 0 ins; 5 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1117.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1117/head:pull/1117

PR: https://git.openjdk.org/jfx/pull/1117