RFR: 8343148: C2: Refactor uses of "PhaseValue::*con*() + PhaseIdealLoop::set_ctrl()" into separate method

[theoweidmannoracle]

This patch introduces the methods `PhaseIdealLoop::intcon` and `PhaseIdealLoop::longcon` which are wrappers for:


ConINode* node = _igvn.intcon(i);
set_ctrl(node, C->root());


and


ConLNode* node = _igvn.longcon(i);
set_ctrl(node, C->root());


Occurrences of this pattern in loopnode.cpp were replaced with the appropriate call to the new methods.

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Commit messages:
 - Add helper methods for zerocon, makecon, and integercon too
 - 8343148: C2: Refactor uses of "PhaseValues::intcon() + PhaseIdealLoop::set_ctrl()" into separate method

Changes: https://git.openjdk.org/jdk/pull/21836/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21836&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343148
  Stats: 112 lines in 5 files changed: 40 ins; 36 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/21836.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21836/head:pull/21836

PR: https://git.openjdk.org/jdk/pull/21836