Add `deliveryMethod` template variable + generic inline mapping syntax to prefund description config

Context

Partners can configure the prefund funds-transfer description string with templates like:

PR {{paymentId}} {{buyAmount}} {{buyCurrency}} {{recipientLegalName}}[20] {{bankCountryCode}}

See docs/prefund-description-config.md for the full reference. Recipient templates expose 8 variables today; there's no way to include the recipient's delivery method (SWIFT vs in-country EFT) in the description.

Two related asks bundled here because they're best designed together:

New deliveryMethod variable.
Generic inline-mapping modifier on the template engine, so a single variable can render different strings per partner without backend code changes.

Part 1 — `deliveryMethod` variable

Add a new template variable on recipient prefund templates.

Source field: recipient.liveData.DeliveryMethodId
Raw values today (from TableConstants.js): W and E
Default rendered output: W → Wire, E → Local

Files to change (variable-map population in each rail adapter, recipient template only):

graphql/src/paymentEngine/rails/InternationalUSDConsWire/InternationalUSDConsWireAdapter.js (~1483–1496)
graphql/src/paymentEngine/rails/InternationalUSDCorpWire/InternationalUSDCorpWireAdapter.js (~1580–1593)
graphql/src/paymentEngine/rails/InternationalFXConsWire/InternationalFXConsWireAdapter.js (~1536–1549)
graphql/src/paymentEngine/rails/InternationalFXCorpWire/InternationalFXCorpWireAdapter.js (~1791–1804)

Part 2 — Generic inline mapping modifier

Extend FormatUtils.populateDynamicString() (graphql/src/utils/FormatUtils.js, ~L429-454) with an inline mapping modifier that lets a template override the rendered string per raw value. This is generic — works on any variable, not just deliveryMethod.

Proposed syntax (engineering can finalize delimiter):

{{deliveryMethod}}                       → "Wire" or "Local"  (default mapping in the adapter)
{{deliveryMethod|W=Swift|E=Local}}       → "Swift" or "Local" (template-level override)
{{deliveryMethod|W=SWIFT|E=ACH}}[6]      → composes with existing [N] width modifier
{{buyCurrency|USD=Dollars|EUR=Euros}}    → works on any variable

Semantics:

If the modifier is present and the raw value matches a key, render the mapped value.
If the raw value doesn't match any key in the modifier, fall back to the default rendered value (i.e. what {{var}} alone would render). This keeps the modifier additive — partners only spell out the cases they care about.
The [N] width modifier applies after mapping: slice the rendered string, not the raw value.
Delimiter (| proposed) must not conflict with any existing template content. If it does, pick another (;, ::, etc.) — flag in the PR.

Caveats

Recipient templates only. Vostro payments have no recipient and no delivery method. Don't add deliveryMethod to the vostro variable map (substitution throws on undefined variables — see existing caveat #2 in the doc).
All 4 flavors (USD/FX × Consumer/Corporate) on the recipient path.
Backwards compatible. Templates without the new modifier render unchanged. The modifier is a pure parser extension.
Unknown variable still throws. The mapping modifier doesn't suppress the existing "unknown variable name" crash — only the per-value mapping is overridable.

Acceptance

{{deliveryMethod}} substitutes to Wire / Local across all 4 recipient prefund templates.
{{deliveryMethod|W=Swift|E=Local}} substitutes to Swift / Local.
{{deliveryMethod|W=SWIFT}}[3] substitutes to SWI (mapping then truncate) when value is W, and to Loc (default mapping then truncate) when value is E.
Generic modifier works on any other variable (test with buyCurrency or bankCountryCode).
Vostro substitution unaffected — vostro templates that don't reference deliveryMethod continue to render correctly.
docs/prefund-description-config.md updated:
"Available variables → Recipient templates" table includes deliveryMethod row.
"Template syntax" table includes the new mapping modifier.
"Suggested templates" section gets one example using the modifier.