Even before this change SockJS sessions always cancelled the heartbeat
task first prior to sending messages. However when the heartbeat task
is already in progress, cancellation of it is not enough and we must
wait until the heartbeat is sent.

This commit adds a heartbeat write lock which is obtained and held
during the sending of a heartbeat. Now when sessions send a message
they still cancel the heartbeat task but if that fails they also wait
for the heartbeat write lock.

Issue: SPR-14356

Issue: SPR-14349
(cherry picked from commit ca12e13e)

Issue: SPR-14345
(cherry picked from commit d51c22a7)

Issue: SPR-14345
(cherry picked from commit c6f63bdb)

(cherry picked from commit f5a9d5e0)

(cherry picked from commit 31aed61d)

Issue: SPR-14305

Issue: SPR-14336
(cherry picked from commit abcfffdd)

(cherry picked from commit 3c987b17)

Issue: SPR-14333
(cherry picked from commit 9131ebbe)

Issue: SPR-14329
Issue: SPR-14323
(cherry picked from commit a9fda3e7)

Issue: SPR-14330
(cherry picked from commit f657952c)

Latest applicable dependency updates (Commons FileUpload 1.3.2, Tomcat 8.0.35, HSQLDB 2.3.4, H2 1.4.192)

(cherry picked from commit 521c41d7)

UriComponentsBuilder allows more efficient (and less restrictive) CORS
origin comparison.

Also introduces a specifically narrowed cloneBuilder() method for
UriComponentsBuilders.

Cherry-picked from 9a52c8.

Issue: SPR-14080

Issue: SPR-14269
(cherry picked from commit 9064d38e)

Issue: SPR-14293
(cherry picked from commit cf0a0cd5)

Issue: SPR-14288
(cherry picked from commit 03affa02)

Issue: SPR-14257
(cherry picked from commit 24f5f368)

Issue: SPR-14298
(cherry picked from commit a979885d)

Issue: SPR-14309
(cherry picked from commit f7f2327f)

Issue: SPR-14311
(cherry picked from commit 2d85accb)

Issue: SPR-14287
(cherry picked from commit dacc31e3)

Issue: SPR-14282
(cherry picked from commit 98eaf05c)

Issue: SPR-14087
Issue: SPR-14272
Issue: SPR-13535
Issue: SPR-13843
Issue: SPR-14164
Issue: SPR-14319

Issue: SPR-14279

Normally heartbeats keep connections from hanging. However in some
cases a connection may hang before a CONNECTED frame is received
and heartbeats are put in place. This commit adds a change to enforce
a 60 limit on receiving the CONNECTED frame.

Issue: SPR-14266

Issue: SPR-14249
(cherry picked from commit 1b1aac91)

Issue: SPR-14244
(cherry picked from commit 08ddd1b3)

(cherry picked from commit 8c139ef4)

Issue: SPR-14241